Fix language reporting dialects as not supported

source/synthDriverHandler.py

@@ -344,6 +344,10 @@ def languageIsSupported(self, lang: str | None) -> bool:
 				or lang == languageHandler.normalizeLanguage(availableLang).split("_")[0]
 			):
 				return True
+		rootLang = languageHandler.normalizeLanguage(lang).split("_")[0]
+		fallbackLang = f"{rootLang}-{rootLang}"
+		if fallbackLang in self.availableLanguages:
+			return True
 		return False
 
 	def initSettings(self):

user_docs/en/changes.md

@@ -62,6 +62,7 @@ We recommend using Windows 11, or if that is not possible, the latest Windows 10
 * When NVDA is configured to update add-ons automatically in the background, add-ons can be properly updated. (#18965, @nvdaes)
 * Fixed a case where braille output would fail with an error. (#19025, @LeonarddeR)
 * Battery time announcements now skip redundant "0 hours" and "0 minutes" and use proper singular/plural forms. (#9003, @hdzrvcc0X74)
+* When a syntesizer has a fallback language for the current dialect, the language of the text been read won't be reported as not supported. (#18876, @nvdaes)
 * Certain settings will no-longer erroneously be saved to disk when running NVDA from the launcher. (#18171)
 * Incorrect information is no longer displayed in braille when navigating the list of messages in Outlook Classic. (#18993, @nvdaes)