Whenever you need a quick access to common HTML selects needs.
The languages select is the first code uploaded to this page. It was created based on the ISO 639-1 standard and a JSON version of it by the Github user jrnk. I just fixed a couple of special characters that got wrongly encoded and added the "Most common" section, based on the 2018 study by w3techs.com about the "Usage of content languages for websites".
CC0 - All the work is available for free to anyone. No attribution required, unless specified by the creators in the credits. All the work is still property of the original authors.
For any problem with the repo or the content, file an issue. I'll be happy to help you!