I don't know about millions of lines of code, but Google Translate existed WELL BEFORE transformer architectures and relied on more traditional statistical machine translation techniques. They later moved to a neural machine translation technique, and then only after that in ~2019/2020 swapped to transformers.

Honestly a lot of us who worked in the translation sector remember NMT as being a huge step up and in some language-pairs even surpassing DeepL at the time.

https://en.wikipedia.org/wiki/Google_Neural_Machine_Translat...