Almost perfect. Only two features lack:
1) Prolong subtitles. It would be great to be able to prolong subtitles for, say, 2-3 seconds when there is no next line, or just until the next line begins otherwise.
2) Always use subtitles stored with the video if available. Currently, if the timestamps in two languages differ, you show one stored and one translated subtitle, even if the video has stored subtitles in the second language (but the timestamps do not match the first subtitle).

你好移植者，请让插件支持字体选择，目前只有一种字体。原作者并没有将插件移植所以请你完成这个工作。Hello porters, please make the plugin support font selection, currently there is only one font. The original author didn't port the plugin so could you please finish this.

Developer should make video subtitles as default instead of translated one.

从Chrome改用到Firefox一直都在用这个扩展，真的很好用，感谢
美中不足的是要是字体自定义能够支持不同字重就好了，目前只能够选择多字重字体里最细的那一个，非常不便于字幕可读性
以及firefox版本的扩展无法更改字体

非常好，還可以下載和看到設置顔色，繼續加油。

想要一次看到两个字幕，提升自己的外语水平。这是个不错的选择

quá tuyệt vời, cảm ơn dev

brilliant add-on,truly solved problem!

使用很简单，效果很满意。
It is easy to use, and the effect is satisfying.

best

Works very well!!!

But I wonder why its original author didn't update the link here on his website?

Works, Great extension)

Simplesmente perfeito!! Só utilizei por alguns segundos, mas totalmente funcional e é exatamente o que procurava, agora ele pega qualquer legenda em ingles e faz tradução simultanea, sem necessidade de ir colocar tradução automatica e selecionar a linguagem do youtube.