#MediaWiki bug 19412 informs us that the parser cannot make hay from a French or a Bengali time or date. As a solution is needed, it is these wonderful people at translatewiki.net who provide us with an even bigger picture; date and time functionality needs its own localisation.
What is wonderful in the proposal by Nikerabbit is that he provides us with the idea what is involved and what use cases are possible.
What this example also shows is that there will be new issues popping up every now and again. For me, the creation of a definitive list of language support and localisation issues is a waste of time. The realisation that issues exist and can be tackled comes first. As we work our way through our known bugs, we will make local time fly and have input methods and web fonts where needed.