My native language is French, and sometimes, I realise I’m thinking in English!
Which is not surprising as my work language is English, I read and watch movies in English.
I cannot remember if I ever thought in Chinese… so here is my question:
Do you ever find yourself thinking in a language that is not your mother tongue?
(BONUS Question: when you think of something, or read a story, do you see images in your head? I do, but it was a big debate in my friends group that some people cannot)
When I learn Chinese, I tend to translate to English rather than my mother tongue. Although translating Chinese to Vietnamese would be easier as the sound and some grammar structures are similar.
I’m Italian and sometimes I find myself thinking in English too!
About Chinese… it’s not something that happens as naturally as with English, but sometimes I “force” myself to think in Chinese just to see if I can formulate the sentences.
When I think about something I usually see images in my head but it’s not something that happens to me ALL the time… if the thought is particularly deep, or emotional, then yes I can see clear images!
The day I think in Italian or Chinese is the day I feel I’ve won at languages 
I used to think in German a lot when I studied German back in the day. I was really into it and did a lot of immersion. I studied French and Spanish but not so much and I didn’t think in those languages very much either. I got into Japanese in my mid 30’s and studied it tons but I don’t think I really thought in Japanese until I moved there and was studying it full time (I studied several hours every day before going though so it seems like I should have thought in Japanese sooner but didn’t). I’ve been studying Korean for about 3 years now and only think in Korean if I force myself to.
Thinking in your target language is really good practice. If you’re already talking to yourself in that language speaking to other people is kind of the same thing.