need some advice, G/F applying for tourist visa to Australia, have a letter from her employer in thai language , informed by Visa application requirements  the letter has to be translated to english, then certified by ?? appropriate thai authority.

?unsure of who/ what authority  to approach to complete this step of certification 

 

Normally the translation has to be certified by the person carrying out the translation to show they are qualified and competent to do so, at least this is the case for a number of other countries.
I don't think you need to get them certified by the MFA, as far as I'm aware they only certify other languages to Thai.