Hi,
Firstly I hope the lawyer are independent and not recommended by the agent. If not you may wish to appoint someone else, it sounds like you need one who speaks good English, there are plenty.
I would be very wary of giving a POA to anyone, particularly if the solicitor is not completely independent.
But you can arrange a POA through a UK solicitor or Notary Public who is empowered as a Commissioner of Oaths.
If I were you I would download the Law Society Conveyancing Protocol - it gives you a checklist of the items you should be looking to verify - don't rely on your solicitor, particularly if they were not recommended from a totally reliable source.
Without being intentionally unkind if they don't speak English and cannot advise regarding a POA why did you appoint them? You may regret not sacking them immediately, but good luck.