For Mandarin pronunciation, go to Google Translate, select Chinese, write in pinyin, click on the suggested hanzi (Chinese characters), and finally click on the »listen« button. Don’t click on the »listen button« before you’ve selected a set of hanzi; the result will be unusable.
If you know the pinyin, the pronunciation part of Mandarin is actually pretty easy to learn, I think, because the number of syllables is limited and there are only four (or five, depending on how you count) tones – and because there aren’t huge numbers of inconsistencies in pronunciation like in European languages. So languages like Mandarin probably benefit the most from text to speech
The benefit over Forvo is that if the word is unique enough, you often don’t need to know the hanzi, because Google Translate will suggest it.
Also, because my command of Mandarin is basically non-existent I’m probably wrong, but I think that if you’re not speaking complete sentences, the importance of rendering tones accurately isn’t as high as you’d probably think if you have read the often repeated bit about, say, ma meaning horse, mother, hemp, and so on. Modern Chinese uses compounds to reduce ambiguity, and combined with knowledge of context, especially something as particular as tea, people will probably still know what term you had in mind even if you just say it all in one flat tone.
So if you don’t need to know the tone, Google Translate is still useful for finding out how to pronounce a syllable. You can also use other websites for this, of course. Probably more efficient. Protip: »Ü« as in »lücha« is written using »v« on the computer.
As Wyardley said, be aware of two issues: firstly that there exist various romanization systems for Chinese languages (e.g. Pinyin and Wade-Giles for Mandarin), and that not all tea-related Chinese words that have entered foreign languages are Mandarin. (Hence cha/chai etc. in some countries, te/tea/tee/teh etc. in others.)
TL;DR If Google Translate doesn’t find the word, try to find an alternative spelling. If you can’t find one, it’s probably not Mandarin but another Chinese language. Can’t help you there.
On a side note, the staff at my local tea shop insist on mispronouncing their Chinese teas
Also, how did this text get so long.