First of all, this is not a recommendation for Best-Matchmaking. If you still want to find your spouse with Best-Matchmaking or you happen to be already involved in such an endeavour, here are a couple of advices I can give to you.
The interpreter is of paramount importance in the process of getting to know your future spouse. And you totally depend on what she translates for you.
An interpreter provided by the agency works for the agency. She might be told to follow other goals than clear interpretation. She might even be involved in or at least silent about trickeries. Even if you pay her directly, you are just a visitor to her. The agency is still the one she depends on to get a job next week. You can find examples on how an interpreter can be involved in Best-Matchmaking's trickery on the Frauds page or read my blog post on my own experience meeting a woman from Best-Matchmaking in the Ukraine.
Further more, my own experience and reports from other clients tell us that interpreters provided by Best-Matchmaking are not always professional. They might struggle with the language as soon as your thoughts became a little more complex than bare small talk.
Your date might also somehow be linked to the money you pay to the agency or the agency's interpreter. Therefore, your payments may influence her behaviour towards you. She might be friends with the interpreter and therefore she would insist in working with her because the interpreter needs the money. It could be far worse though. Study the Frauds page for possible entanglements.
For these reasons, I suggest you to organise an trustworthy and professional interpreter yourself. You can already do that for Skype video calls. If you are already in the foreign country, the city's official tourist infomation can help you to find a trustworthy and professional interpreter.
The agency or your spouse might insist in the interpreter from the agency. You can still consider to bring your own independent interpreter besides the one provided by the agency.
Get an Ukrainian SIM card. It just costs about 10 EUR. You can communicate with your spouse far cheaper than by international roaming. You will also have access to mobile internet usually already included for one month.