Gemini 3.8 Flash TTS supports 130+ languages: multilingual ad reads

Gemini 3.8 Flash TTS (gemini-3.8-flash-tts) is documented with more than 130 languages, the largest count among the voice models I read this week; Flash-Lite TTS lists more than 100. Both detect the language automatically. For a multilingual ad campaign that means one API and one set of voices can cover many markets. It does not mean every language sounds equally good, and a language count is not a quality score.

What Google states

A workflow for a multi-market ad

• Localise the copy first. Translating an ad word for word usually breaks rhythm and the call to action. Have a native writer adapt it.
• Pick one voice per market from the prebuilt set and keep it fixed across the campaign.
• Write numbers, prices, brand names and URLs the way you want them read. Auto detection can guess wrong on a short line that mixes scripts, so test those lines.
• Render each language, have a native listener check it, and keep a pass/fail log per line.
• Check the output length against the slot in the edit before you commit the schedule.

Where Sume stands

Sume does not ship Gemini TTS. Its TTS Router serves Cartesia Sonic only, so any market Sonic does not cover cannot be served from the TTS catalog; check the language list in the catalog (GET /v1/tts-router/models) before you plan a market. A Sume voice has a primary language and the API returns 409 tts_voice_language_mismatch when a request's language disagrees, so a copy-paste of the wrong language does not reach a paid render without a confirmation.

So for a 100-plus-language campaign, use Google directly. For a handful of major markets that Sonic covers, with the render, billing and receipts in one place, Sume is the managed alternative.