The vast majority of users won't recognize the tag hmrc as meaning tax-uk, so if someone says something applicable to other localities they'll miss it. Specifically if you're from elsewhere in Europe and want to compare UK tax treatment vs your own country's vs other European countries. Or thinking of contracting in the UK.
(We don't want tags for acronyms of 220+ different national or regional tax bodies do we?)
Practically none of us would recognize a question tagged 'Skatteverket' or 'Cadastro de Pessoas Físicas (CPF)' as being synonymous with 'taxes-se' or 'taxes-br'. CPF has 24 possible meanings, btw, so you can't really google it. Why be cryptic, when you can be clear?
Shouldn't we keep the tags as clear and self-explanatory as possible, avoiding location-specific and foreign-language acronyms wherever reasonable?