I can't find this crucial information in the official docs or here. Which natural languages are supported by the service? Which languages will be supported in the near future? I'm interested in POS tagging with lemmatization and dependency parsing. I tried analysing Russian, Polish and even Italian sentences and got a 400s (“The language ru is not supported for syntax analysis” etc.). If advertising a service as multilingual, it would be fair to admit which languages are supported before having to register and enter credit card details.
Your discovery is correct. On this page it states "The Cloud Natural Language API currently supports English, Spanish, and Japanese for sentiment analysis, entity analysis, and syntax analysis."
The "Google Cloud Natural Language API" web page states under multi-lingual support: "Combine the API with our Google Cloud Speech API and extract insights from audio conversations". The languages supported by the "Google Cloud Speech API" service are listed here. Russian, Polish, and Italian are supported.
Apparently you can use the Speech API with eighty-nine languages but only use the Natural Language API on three languages!