Internationalization on the web – why is it so bad?

Totally agree. It's a shame few websites pay attention to the Accept-Language header.

Although I'm not fluent in English I do always prefer it to local languages when it comes to nonlocal websites since even giants like Facebook and Google can't get their translation right:

1. Almost always translated version is substantially outdated.

2. A lot of inconsistency like using different synonyms in different places for the same word in English locale.

3. Some sentences are just not translated.

Please take a look at Tr8nHub.com

Our platform with all the SDKs (for mobile, web and desktop) addresses all of the concerns you've raised. The SDKs will choose language based on your preferences in the browser, mobile device or OS, yet you are also given a choice to override the defaults by choosing a specific language.

There's a reason it's called "the web"