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feat(prompts): locale-native reinforcement preamble for non-English UIs (#1118 follow-up)

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`base.md` stays the single source of truth (English meta-language,
DeepSeek V4 is natively multilingual, prefix-cache stable across
users in the same locale). For non-English UI locales we now prepend
a short locale-native passage so the model's first exposure to the
prompt is an explicit "think and reply in {locale}" directive in the
user's own writing system — defeats the failure mode reported in
#1118 and visible in the recent WeChat screenshot where a user with
`locale = zh-Hans` configured still got English thinking because the
task context (Rust code, English log lines) overpowered the inferred
`## Environment.lang` signal.

Locales supported (matched against `PromptSessionContext.locale_tag`,
which the caller resolves from `Settings`):

* `zh-Hans` / `zh-CN` / `zh` — Simplified Chinese preamble
* `ja` / `ja-JP` — Japanese preamble
* `pt-BR` / `pt` — Brazilian Portuguese preamble

English (and any unmatched locale) returns `None` and the system
prompt is byte-identical to v0.8.28 — so this is a strict additive
change for non-English users.

Each preamble is ~6-8 lines and explicitly:

* names the runtime ("DeepSeek TUI") so the model knows it's not
  switching personas
* declares the directive for BOTH `reasoning_content` and the final
  reply (the V4 knob that #1118 hinges on)
* preserves tool-name immutability (`read_file`, `exec_shell`,
  paths, env vars, CLI flags, URLs stay in their original form)
* handles mid-session language switches (next-turn switching)
* defers to explicit user override ("think in English" etc.)

Three new tests pin the contract:

* `locale_reinforcement_preamble_returns_native_script_for_supported_locales`
  — preamble must be in the locale's native script, must mention
  `reasoning_content`, and must call out tool-name immutability;
  English/unknown locales must return `None`.
* `system_prompt_prepends_locale_preamble_for_zh_hans` — the
  preamble must appear *before* the English base prompt body in
  the assembled system prompt (attention precedence + cache
  ordering both depend on this).
* `system_prompt_skips_locale_preamble_for_english` — English
  locale must produce a byte-identical prompt to the pre-feature
  behavior (no zh / ja / pt strings anywhere).

Prefix-cache impact: per-locale cache shards stay intact (a
zh-Hans user's prompt shares the preamble across turns; an English
user's prompt is unchanged). Cross-locale cache is invalidated,
which is correct — different users in different locales were never
sharing cache for the right reasons.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
This commit is contained in:
Hunter Bown
2026-05-10 21:11:37 -05:00
parent f03df9d3e0
commit 47f6d69e58
1 changed files with 193 additions and 0 deletions
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crates/tui/src/prompts.rs
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@@ -133,6 +133,67 @@ fn load_handoff_block(workspace: &Path) -> Option<String> {
/// "When NOT to use" guidance, sub-agent sentinel protocol.
pub const BASE_PROMPT: &str = include_str!("prompts/base.md");
/// Optional locale-native reinforcement preamble prepended to the system
/// prompt when the user's UI locale is non-English.
///
/// `base.md` itself stays English (single source of truth, model is
/// natively multilingual, prefix-cache stable across users in the same
/// locale). For non-English locales we prepend a short locale-native
/// passage so the model's first exposure to the prompt overrides the
/// "match user message language" English directive with an explicit
/// "use {locale}" instruction in the user's own writing system. Reduces
/// the model's reliance on inferring intent from `## Environment.lang`
/// — which previously got overpowered by overwhelmingly English task
/// context, the symptom reported in #1118 and visible in the WeChat
/// screenshot that prompted this change.
///
/// The list is intentionally short (only locales the TUI ships UI
/// strings for: `zh-Hans`, `ja`, `pt-BR`). Other locales fall through
/// to `None` and get the English-only directive, which is the same
/// behavior as before this change.
pub(crate) fn locale_reinforcement_preamble(locale_tag: &str) -> Option<&'static str> {
match locale_tag {
"zh-Hans" | "zh-CN" | "zh" => Some(LOCALE_PREAMBLE_ZH_HANS),
"ja" | "ja-JP" => Some(LOCALE_PREAMBLE_JA),
"pt-BR" | "pt" => Some(LOCALE_PREAMBLE_PT_BR),
_ => None,
}
}
const LOCALE_PREAMBLE_ZH_HANS: &str = "## 语言要求\n\n\
你正在 DeepSeek TUI 中运行。无论任务上下文（代码、错误日志、文件名）\
是英文，无论系统提示的其余部分是英文，你都必须用简体中文进行 \
`reasoning_content`（内部思考）和最终回复。代码、文件路径、工具名称\
（例如 `read_file`、`exec_shell`）、环境变量、命令行参数和 URL \
保持原样 —— 只有自然语言散文要切换到简体中文。\n\n\
如果用户在会话中切换到另一种语言，从下一轮开始跟随切换。\
如果用户明确要求（例如 \"think in English\"），则覆盖此规则。";
const LOCALE_PREAMBLE_JA: &str = "## 言語要件\n\n\
DeepSeek TUI を実行しています。タスクコンテキスト（コード、エラーログ、\
ファイル名）が英語であっても、システムプロンプトの他の部分が英語で\
あっても、`reasoning_content`（内部思考）と最終的な返信は日本語で\
行ってください。コード、ファイルパス、ツール名（例：`read_file`、\
`exec_shell`）、環境変数、コマンドライン引数、URL は元のまま —— \
自然言語の文章のみ日本語に切り替えます。\n\n\
ユーザーがセッション中に別の言語に切り替えた場合は、次のターンから\
それに従ってください。ユーザーが明示的に要求した場合（例：\
\"think in English\"）はこのルールを上書きします。";
const LOCALE_PREAMBLE_PT_BR: &str = "## Requisito de Idioma\n\n\
Você está rodando dentro do DeepSeek TUI. Escreva tanto \
`reasoning_content` (seu pensamento interno) quanto a resposta final \
em português do Brasil, mesmo quando o contexto da tarefa (código, \
logs de erro, nomes de arquivos) estiver em inglês e mesmo quando o \
resto do system prompt for em inglês. Mantenha código, caminhos de \
arquivos, nomes de ferramentas (por exemplo `read_file`, \
`exec_shell`), variáveis de ambiente, flags de linha de comando e \
URLs no formato original — apenas a prosa em linguagem natural muda \
para português do Brasil.\n\n\
Se o usuário mudar de idioma no meio da sessão, mude no próximo turno. \
Se o usuário pedir explicitamente (por exemplo, \"think in English\"), \
isso sobrescreve esta regra.";
/// Personality overlays — voice and tone.
pub const CALM_PERSONALITY: &str = include_str!("prompts/personalities/calm.md");
pub const PLAYFUL_PERSONALITY: &str = include_str!("prompts/personalities/playful.md");
@@ -371,6 +432,16 @@ pub fn system_prompt_for_mode_with_context_skills_session_and_approval(
// Load project context from workspace
let project_context = load_project_context_with_parents(workspace);
// 0. Locale-native reinforcement preamble (#1118 follow-up). When the
// user's UI locale is non-English we prepend a short native-script
// passage so the model's first exposure to the prompt is an explicit
// "think and reply in {locale}" directive in the user's own writing
// system — defeats the "task context is English, so the model thinks
// in English even though `lang: zh-Hans` is set" failure mode that
// PR #1398 partially addressed. English (and unknown) locales get
// `None` and keep the previous behavior unchanged.
let preamble = locale_reinforcement_preamble(session_context.locale_tag);
// 1–2. Mode prompt + project context.
// `load_project_context_with_parents` auto-generates .deepseek/instructions.md
// when no context file exists, so the fallback should always be available.
@@ -383,6 +454,10 @@ pub fn system_prompt_for_mode_with_context_skills_session_and_approval(
mode_prompt
};
if let Some(preamble) = preamble {
full_prompt = format!("{preamble}\n\n{full_prompt}");
}
if session_context.project_context_pack_enabled
&& let Some(pack) = crate::project_context::generate_project_context_pack(workspace)
{
@@ -539,6 +614,124 @@ mod tests {
assert!(block.contains("- shell:"));
}
#[test]
fn locale_reinforcement_preamble_returns_native_script_for_supported_locales() {
// English (and unknown locales) get None — the existing English
// directive in `base.md` is sufficient.
assert!(locale_reinforcement_preamble("en").is_none());
assert!(locale_reinforcement_preamble("en-US").is_none());
assert!(locale_reinforcement_preamble("fr-FR").is_none());
assert!(locale_reinforcement_preamble("").is_none());
// zh-Hans (and the de-facto equivalents the TUI accepts) get a
// native-script preamble. The text must explicitly mention
// `reasoning_content` (the V4 knob this is meant to steer) and
// preserve tool-name immutability — those are the load-bearing
// claims behind the #1118 fix that someone could quietly
// delete in a future translation pass.
for tag in ["zh-Hans", "zh-CN", "zh"] {
let preamble =
locale_reinforcement_preamble(tag).expect("zh-Hans preamble should exist");
assert!(
preamble.contains("简体中文"),
"zh preamble must be in Simplified Chinese: {preamble:?}"
);
assert!(
preamble.contains("reasoning_content"),
"zh preamble must steer reasoning_content: {preamble:?}"
);
assert!(
preamble.contains("read_file"),
"zh preamble must call out tool-name immutability: {preamble:?}"
);
}
let ja = locale_reinforcement_preamble("ja").expect("ja preamble");
assert!(ja.contains("日本語"), "ja preamble must be in Japanese");
assert!(ja.contains("reasoning_content"));
let pt = locale_reinforcement_preamble("pt-BR").expect("pt-BR preamble");
assert!(
pt.contains("português do Brasil"),
"pt preamble must call out pt-BR explicitly"
);
assert!(pt.contains("reasoning_content"));
}
#[test]
fn system_prompt_prepends_locale_preamble_for_zh_hans() {
// Build the full system prompt with locale=zh-Hans and assert
// the native-script preamble shows up *before* the English
// base-prompt body. Cache stability and attention precedence
// both depend on this ordering.
let tmp = tempdir().expect("tempdir");
let text = match system_prompt_for_mode_with_context_skills_session_and_approval(
AppMode::Agent,
tmp.path(),
None,
None,
None,
PromptSessionContext {
user_memory_block: None,
goal_objective: None,
project_context_pack_enabled: false,
locale_tag: "zh-Hans",
},
ApprovalMode::Suggest,
) {
SystemPrompt::Text(text) => text,
SystemPrompt::Blocks(_) => panic!("expected text system prompt"),
};
let preamble_marker = "## 语言要求";
let base_marker = "You are DeepSeek TUI";
let preamble_pos = text
.find(preamble_marker)
.expect("zh-Hans preamble should be present");
let base_pos = text
.find(base_marker)
.expect("base prompt should be present");
assert!(
preamble_pos < base_pos,
"locale preamble must precede the English base prompt (preamble={preamble_pos}, base={base_pos})",
);
}
#[test]
fn system_prompt_skips_locale_preamble_for_english() {
// English locale → no preamble injected. Asserts the
// "preamble is opt-in for non-English" invariant.
let tmp = tempdir().expect("tempdir");
let text = match system_prompt_for_mode_with_context_skills_session_and_approval(
AppMode::Agent,
tmp.path(),
None,
None,
None,
PromptSessionContext {
user_memory_block: None,
goal_objective: None,
project_context_pack_enabled: false,
locale_tag: "en",
},
ApprovalMode::Suggest,
) {
SystemPrompt::Text(text) => text,
SystemPrompt::Blocks(_) => panic!("expected text system prompt"),
};
assert!(
!text.contains("语言要求"),
"English locale must not get a zh preamble: {text:?}"
);
assert!(
!text.contains("言語要件"),
"English locale must not get a ja preamble: {text:?}"
);
assert!(
!text.contains("Requisito de Idioma"),
"English locale must not get a pt-BR preamble: {text:?}"
);
}
#[test]
fn language_section_carries_reasoning_content_directives_for_1118() {
// #1118 ("Language has been configured to Chinese, but thinking