I think good questions for community call. Some info here and in the linked PR- https://github.com/brave/brave-browser/issues/18593#issuecomment-951706548
Looks like not a client side but through API calls to https://translate.brave.com/. May be @SaltyBanana can give an insight.
What is the ācommunity call?ā
Hey, Iāll answer that one. Every Tuesday around 5pm ET (2pm Pacific), Luke Mulks and various people from Brave hop on Brave Talk to discuss projects they are working on, give updates on various statistics, and they answer questions from Users. Itās only an hour but itās been incredibly educational and helpful. Thatās called the weekly BAT Community Call. As sharing with people, Iāve shortened it to Community Call.
I donāt know who initiated specifically or why, but I know itās done through a group called BAT Brigade that has a Discord anyone can join. BAT Brigade in itself actually hosts a variety of events, from Friday Night Trivia (where you can earn BAT by answering questions correctly), weekly Twitter Spaces (which I just learned is another call type of thing), and other events.
If you want to listen in on past recordings, you can do so by checking out the channel at https://youtu.be/oSPThAOTk04
If youād like to participate in the call, you do that at https://talk.brave.com/WELCOME--TO--THE--WEEKLY_BAT-COMMUNITY_CALL
If wanting to join BAT Brigade, an invite link is https://discord.com/invite/9xsktrZmHK
Btw, on listening to past calls, Iād definitely check out the calls below:
This one below was packed with info regarding mobile and the future of Rewards in general.
If you care about Search, check out https://youtu.be/3I3s_kELZtQ
Then maybe https://youtu.be/R3BZssNyH0k
Out of those though, definitely most important IMO was one with Anthony Keane and Chriscat, which I have playable (embedded) here this this post/comment.
See how Vivaldi has good documentation done for user FAQ
Both are doing the same thing, using Lingvanex proxy api to do it. Brave has one twitter post made while vivaldi has proper notes for users to know, how it works and if it is privacy friendly or not.
Very interesting. I hope Brave makes some announcement when the feature hits release. But I donāt think it will be as near exhaustive as Vivaldiās. Brave has a lot of catching up to do after all.
It was announced in the release notes for version 1.43.88, though I had to go into the flags and turn on the translator feature there too.
Oh, my bad. Missed that.
Just so you know @chh_68 , I passed this question on to Sampson over on Twitter. He responded with the answer below:
Translation is done server-side for both Brave and Vivaldi; neither uses a third-party endpoint. Both use Lingvanex, though Brave has a 2x lighter payload which also preserves line-breaks in the content (translate http://sampson.codes/brave/tests/translate/ā¦ in both browsers for a quick demo).
@Saoiray and @chh_68: I can confirm that Brave translates the mentioned URL and does not break the line breaks, whereas Vivaldi has the translated text in a single line.
I have never encountered this behavior after using Lingvanex on Vivaldi hundreds (if not thousands) of times. The line breaks are lost because he dumps the content as raw text and did not use correct HTML formatting.
I do not understand the relationship between Lingvanex and Transifex. Why both? What is the purpose? If Brave is using Lingvanex why could I only find a couple of issue reports at Brave GitHub referencing Transifex. An explanation would be helpful because I am confused about the Lingvanex vs Transifex references being made.
Also, I do not see Lingavanex functionality (features) as documented at https://lingvanex.com/user-manual-windows/. Is a full Lingvanex implementation planned for a later date? Or is the functionality already present natively and I just donāt know how to activate it?
Many of the Lingvanex features would be nice to have like the abilty to translate mixed text pages natively. Right now, for example, if I open a topic in Brave Community that has a post in a non-English language, I do not get a translation button (should I?) Also the image translate and voice recognition features are nice. Will this be a premium service offered to Brave Browser users? I would be interested especially if native vs 3rd party app download and doubly if I could purchase the service with vBAT/BAT. 
Other Feedback:
Translate in Release version does not work unless the flag(s) are enabled at brave://flags. If the flags are not enabled, I get the prompt to install Google translate when enable Offer to translate pages that aren't in a language you read at brave://settings/languages The feature does work in Beta just by enabling the option at language settings which is weird since Beta is still at 1.43.79 and Release at 1.43.89.
I really like this feature even without all the bells and whistles. Very nice to go to a page and just press a button to get a page translated without having to install an extension or copy/paste the text to a translator. Thank-you to the Brave team for implementing this feature! Well done. 
I might have seen wrong somewhere. Iāll trust what @talgeeze said for the moment. I mean, I ended up with the link I did somehow when I was looking through Github and other things for updates on Brave Translate, but I couldnāt tell you how I ended up with it right now.
Not quite sure how that works. Feel free to hop on Twitter and try to ask for more info. Otherwise Iāll be digging for it on Tuesday I think. Just so you can see his Twitter response with the info I said earlier:
https://twitter.com/BraveSampson/status/1565754782467629056?s=20&t=g5hBnSB8h7trp0cOKQrW3w
I do not do twitter, or social media in general. I will hop over to read posts on a social media site if it is something I can read without logging in but otherwise, not gonna happen. If you do post a question per this, just recap or provide link to response please.
Also, not sure what reference to Tuesday meant? Is that when the community call takes place? Edit: and nm, went back and reread information and indeed call takes place on Tuesday, so that is probably what you are referencing. lol
Lingvanex is a translation engine Brave uses for their website translation feature.
Transifex is a localization management platform mainly used for localizing user interface. Itās like Github, but for translating stuff instead of coding stuff.
They offer many features, but availability will vary depending on third-party implementation (aka how much money Brave is willing to spend on the service).
Only full page translation is currently supported. I have not seen anything about supporting partial translation (like Vivaldi) or on the fly translation (like the Google Translate and Deepl extensions).
Found info at Brave GitHub. I stay in the brave-browser repository so much, I forget sometimes to look for issues in other repositories. Such was the case in this instance. Really no meaningful information from an end-user standpoint, but integration issue report for Lingvanex is there.
Funny thing, when I went back to brave-browser and searched issues, I did pull up a closed issue with a link to the go-translate repository this time. No idea. Maybe I just overlookedā¦? Maybe itās magic? Who knows. 
@talgeeze Thank-you for the information! Makes much more sense to me now. Also nice to know I am not missing any available features.
Yes, I know it was mentioned in the release notes, what I meant was proper blog post going into detail on how it works exactly, just like vivaldi and firefox explained their new translate feature.
Release notes told us about the translate feature is in this release, but it never told us how it works. The twitter post only mentioned Lingvanex from which I got to personally know that it is working same as Vivaldi.
This partial translation is a cool feature. Like Chocoholic said about just translating alien posts on a page. Hope Brave implements that. Not sure if even Google Translate could do that.
Also, I think a Topic could be created where users can post burning questions to be asked in the Community Call. Could be fun.
Iāve used many solutions out there so they have all pros and cons:
Hello, I have the same issue with Brave built-in translator:
it wonāt appear on many websites, while Vivaldiās built-in translator shows up everywhere.
What to do about this issue?