Naturally, it is the lawyer who is the key to filing a lawsuit abroad. Generally speaking, unlike in Japan where all the lawyers are of high quality, there are lawyers abroad who are not very capable.
Basically, the debt collection lawsuit is said to have a high probability of success. If you can prove that there is a claim and that it is unpaid, there is relatively little room for refusal. However, if there is a competent lawyer on the debtor side, you may lose the case. Communication is important in this respect.
English language skill is important for communication but more importantly, it is important not to leave unknown things or questions as they are. I think the point is largely due to differences in culture and thinking, there are lawyers overseas who are willing to answer only if they ask questions about the client's disadvantage and the possibility of losing charges.
It is also common to sign the Power of Attorney for delegation but it is also important to specify the scope of the delegation. The risk is too high for a blank power of attorney.
In these respects, it would be better to have your partner's overseas lawyers be introduced through your own legal counsel or to use a large international legal corporation.