Looking for an alternative to Immersive Translate, I found an open-source browser extension: JianYue Translate (简约翻译).
I mainly use it to read English pages, and its bilingual webpage translation is what I reach for most. Like Immersive Translate, the original and translation show together, which is handy for reading docs and tech articles; you can also select a word or sentence to translate on the fly without switching tabs.
It also supports YouTube bilingual subtitles, so you can follow both the original and translation while watching English videos. The interface is clean and focused, without much distraction.
Compared with Immersive Translate, JianYue Translate feels like a worthwhile open-source option: it covers bilingual webpage translation, select-to-translate and video subtitles, and supports multiple translation services and custom config. If you read English pages often, give it a try.