I'd just like to mention that England does not have an "official language" - there has never been an Act to declare any language official. As a consequence, the language of the English Court is taken to be the "official language" - ie, French ! On the other hand there are three Official Languages of the EEC, viz. English, French, and German - so English became official when the UK joined, but only outside the UK. The strange thing is that Scotland similarly has never had an official language, and the Scottish court language was also French, so if Gaelic becomes official, English will be the unofficial language of Scotland.
It may also be of interest that a movement in Spain has forced recognition of Catalan as an official language, and that many official documents (such as licenses for pharmaceuticals, which is how I know) now have to be rendered in both Catalan and Castilian, which is keeping a lot of translators in gainful employ!