Error selecting language in google TTS

Need help with changing language for google TTS.
I would like to select slovenian language (it is in the list of supported languages)… but, when I check configuration… there is error:

Invalid config for [tts.google]: value is not allowed for dictionary value @ data['language']. Got 'sl'. (See ?, line ?). Please check the docs at https://home-assistant.io/components/tts.google/

I also try with ‘sl-SI’… but the same error.

I read somewhere that I should add sl-Sl in google.py … but I run hassio and i don’t know how to do that.

I don’t use hassio, but I’m pretty sure it still supports custom components. If that’s true, then you can grab a copy of google.py and place it at <config>/custom_components/tts/google.py, where <config> is your HA configuration directory (i.e., the directory containing configuration.yaml.) Then edit the SUPPORT_LANGUAGES list and see what happens.

Thanks for advice… I try it and there is no more error when checking configuration…

But it still doesn’t work.
When I send to mediaplayer.mpd to say ‘nekaj’ I get in log this error:

Error on init tts: No TTS from google for 'nekaj'
22:02 components/tts/__init__.py (ERROR)
Error 404 on load url https://translate.google.com/translate_tts?ie=UTF-8&tl=sl-SI&q=nekaj&tk=345964.247337&total=1&idx=0&client=tw-ob&textlen=5
23:00 custom_components/tts/google.py (ERROR)

Obviously it’s not error on HA side but link on google translate… It doesn’t work with slovenian language…

I also notice that in HA docs for Google text-to-speech there is link for supported languages… but it is for Speech-to-Text…not Text-to-speech, which is here: https://cloud.google.com/text-to-speech/docs/voices