If you get an CELTA (RSA Preparatory Certificate) it is accepted throughout Europe, Asia and the UK. English Language Schools in the UK, in fact, prefer this certification to other forms. There's a link here to the Cambridge site:
Cambridge ESOL: Certificate in English Language Teaching to Adults (CELTA)
The Trinity College London equivalent certificate is also widely accepted in language schools in UK and abroad. Here's the link for that:
Trinity College London
In general, I think that UK employers prefer the Cambridge certificate.
Hope this is useful for you.
Clare
ELTgames.com