https://github.com/yt-dlp/yt-dlp is gonna be the go-to tool for any YouTube downloading, but I don’t have much experience with frontends for it. I use Tartube for archiving channels, but it can be a bit byzantine and might be overkill for what you need–plus, there’s a decent chance you will need to manually enter some yt-dlp options anyway (although only during the setup process). That being said, it’s the only one I have experience with, so it’s the one I’ll recommend!
Couple of clarifying questions:
When you say “download a YouTube channel in a particular language”, do you just mean a general monolingual channel (e.g. Masahiro Sakurai’s Japanese channel), or do you mean a channel that has videos with multiple audio tracks (such as this video with three different language tracks)? Both are doable, but I think you’ll need to add an actual command line flag for the latter whereas the former should be achievable pretty simply through Tartube’s GUI.
Are the subtitles you’re talking about added by the uploader, or are they auto subs (in this case, auto subs that are auto translated)? Both are easily achievable through the GUI, just slightly different instructions for either one. Also, depending on the scope of things, the simplest approach might be to simply download all subtitles (may not want to do that for like a MrBeast video with a dozen subtitle tracks), which also sidesteps the possible issue where the language of tracks isn’t properly indicated by the uploader.
When you say “put all streams for a single video together”, do you mean that you don’t want the video and audio tracks merged into a single file, or just that when you try to download the video you get a pre-merged file that doesn’t contain the tracks that you want? Was a little confused by this part.
I know you’re looking for a GUI solution, but while I wait for clarification I might as well drop a basic yt-dlp command to give you an idea of the parameters we’re dealing with (here I’m assuming separate audio tracks and uploader-added subs):
–format bv+ba[language=ja]: gets the “best” video track and Japanese audio track (for a 4K video yt-dlp prefers the VP9 encode, but if it’s a video with a lot of views there may also be an AV1 encode–if you want that AV1 encode you have to explicitly opt for it by using bv[vcodec^=av01] instead of plain bv) –sub-langs en: downloads English subtitle(s) –write-subs: write subs to an external file (as opposed to embedding them) –convert-subs srt: converts subs to srt format, if possible --download-archive channel_archive.txt: writes the IDs of successfully downloaded videos to the specified file channel_archive.txt. If you re-run this command, these videos will be automatically and very speedily skipped over without needing to fetch any additional information. Even without this option, yt-dlp is smart enough to skip over videos that have already been downloaded (assuming the output filenames will be the same), but it will go through the entire process of fetching all the video information for each video up to the point it is about to start downloading, which is a huge waste of time if you’re just updating a channel archive and need only the newest three videos.
Everything in that command (except for the audio track bit, to my knowledge) can be handled in the Tartube GUI in relatively simple fashion, provided you know which menus to dig into.
edit: forgot the URL in my command, kinda important!