Video language

YouTube will guess this if you leave it alone, and the guess is wrong often enough to matter. Set it by hand in the upload flow or in video details. Everything downstream depends on it. Automatic captions transcribe in the language you declared, translated captions and titles work from that base, and auto dubbing produces a translated audio track from it. Setting it correctly improves auto-dubbing accuracy, and a wrong setting produces gibberish captions that help nobody and read badly to anyone relying on them. Check the back catalogue too, since older uploads were often published before anyone thought about the field.