fix(translate): improve auto translate language detection (#9375)

fix(translate): 调整语言检测阈值并增加回退逻辑

当文本较短时使用LLM检测语言，较长时优先使用franc检测
当franc检测失败时回退到LLM检测
同时将LLM检测的文本长度限制从50提高到100

src/renderer/src/utils/translate.ts

@@ -29,7 +29,15 @@ export const detectLanguage = async (inputText: string): Promise<TranslateLangua
   switch (method) {
     case 'auto':
       // hard encoded threshold
-      result = estimateTextTokens(text) < 50 ? await detectLanguageByLLM(text) : detectLanguageByFranc(text)
+      if (estimateTextTokens(text) < 100) {
+        result = await detectLanguageByLLM(text)
+      } else {
+        result = detectLanguageByFranc(text)
+        // fallback to llm when franc fails
+        if (result === UNKNOWN.langCode) {
+          result = await detectLanguageByLLM(text)
+        }
+      }
       break
     case 'franc':
       result = detectLanguageByFranc(text)
@@ -48,7 +56,7 @@ const detectLanguageByLLM = async (inputText: string): Promise<TranslateLanguage
   logger.info('Detect langugage by llm')
   let detectedLang = ''
   await fetchLanguageDetection({
-    text: sliceByTokens(inputText, 0, 50),
+    text: sliceByTokens(inputText, 0, 100),
     onResponse: (text) => {
       detectedLang = text.replace(/^\s*\n+/g, '')
     }