Job offer received in Jakarta - help

As far as I know there isn't a tax agreement between the UK and Indonesia but you can check this through the UK gov site online. You are legally working here then you will get a tax code and have to pay tax and finding out how much might be a challenge but your employer will tell you. You should also ask about when you leave and how the tax process ends as again that might not be clear and being indoensia won't be clearly explained.
Sick entitlement isnt a given here although there should be some mention of it. You should ask and then ask why not.
Employers do make the wording in English here quite complicated so ask them for the Indonesian copy of as they should have and try find a translator in your home country who could decipher it for you. I have seen contracts here full of big words but no message and when asked it's all smiles and nods.
You should know that verbally discussing the contract can also be regarded as part of the final terms and conditions yet they aren't written down so recorded all meetings you have over this contract.
Ultimately if ask questions your employer should tell you the truth or what they think you want to hear so record it and if you still like the offer and agree to it whatever the outcome then anything that happens will be your issue not theirs.
I am not trying to scare you just explaining my opinions from contracts seen and heard about whilst being here.

The big message from this is, don't expect UK employment law because you won't get it.
That's the downside. The upside is salaries are very often very, very high when compared to locals so you're very well off financially.