After uploading a video on Commons, I had a hard time trying to figure out how to add subtitles in another language. I wonder if there are any efforts aimed at making this process simpler, so more people can add subtitles.
Considering the amount of videos there are out there, am I crazy to think that people would be more likely to contribute if this tool existed? Feel free to point me to the tool or the procedure if it exists. 
I found your input only seconds ago, and totally share your concern. As I translate English-Japanese, it means I need to remember another challenge: that per second three characters are the maximum I can squeeze in, or viewers need to slow down playing rate to read the subtitles.
On top of that, double-byte characters are “fatter” than Latin scripts. It means fewer characters are allowed for a single line, and two lines are the max for readability.
Those two points are emphasized by professional subtitle translators on the web in Japanese language. Too bad it is not a universal wisdom yet, or I’d love to see it as instructed on Commons.
我印象中好幾年前有看到同事在翻譯維基媒體影片的時候，曾經見過一個外部網頁可以顯現翻譯原文與時間碼，然後可以在該網頁上面加上不同語言的翻譯，之後便能導出翻譯過後的字幕時間碼，就能上傳到 Commons 上。但這已經是近 10 年前的事情，我已經忘記那個網站是什麼了。
不過如果目前沒有可行的方法的話，或許可以先把這件事情記下來，然後藉由明年 Community Wishlist Survey 的時機提案，以此發展出一個字幕翻譯流程。