Out of interest, why is it ‘unconventional’ ? We are qualified professionals doing a job for which we get paid. We need to turn up on time and do our job well. We often we live outside our home country sure but not always.
Anyway may I point you in the direction of this thread which covers a lot of stuff although the OP was referring to a particular advert they’d seen.
Qualification - yes get one, it’s the first way for language schools to weed out unprofessional candidates and vice versa. Most EFL/ ESL* qualifications are internationally recognised. You learn ‘how’ to teach, not just grammar but language skiils too.
Language skills - some knowledge of or ability to pick up other languages is a plus for your private life if you live abroad but the whole idea of EFL is that only the target language is used in the classroom and once qualified you should be able to teach speakers of all languages equally well. Some people see the teacher’s monolingualism as a distinct advantage - they teach a pure communicative method rather than falling into sloppy translation.
Most EFL teaching ‘abroad’ is aimed at classes sharing a common language but in the anglophone countries you have Japanese speakers, Polish speakers, Brazilian Portuguese speakers together in the same room - bravo to any teacher who can help them all by using translation !
Where are you ? If you are in the UK or Ireland you want to be looking for places which offer the Cambridge CELTA or Trinity TESOL certificates. REputable schools will always expect you to have a teaching qualification. For job adverts The Guardian newspaper on a Tuesday and the EFL Gazette.
My e-mail is in my user profile (not sure if guests can access this) but drop me a line if you have specific questions (if you can’t find it ask here).
*In reality there is dlitle difference between the two but EFL - English as a Foreign Language is aimed at people who need English but don’t live in an English speaking country, ESL - English as a Second Language is more for those living in an Anglophone country. The latter, ESL, seems to me to be more common in North America.