I think it's more a matter of knowing what phonemes are available in each language (probably have to look at a phoneme chart for both) and knowing that results won't be perfect/it's very time-consuming. For example, there are only 5 vowels in Japanese and each only has 1 way to pronounce them. But English has A LOT of different A's alone, not counting other O's and I's, etc. Japanese only has a special R sound that's a combination of L/R/D due to tongue placement, so know that you can't easily make a hard R sound or an L sound English has when you are using a Japanese bank.