All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
A mother has no right to force her son to marry again, however, he should be soft and gentle in objecting her, and he should convince her in a gentle manner that he does not need to marry again, and that the difference of nationality is not a problem as long as there is an understanding between the two spouses and they observe the Limits of Allaah.
Therefore, if this man is able to marry a second wife, and this marriage does not cause any harm to him, then it would be more appropriate for him to marry a second wife as a sign of obedience to his mother.
For more benefit, please refer to Fataawa 84942 and 123554.
Allaah Knows best.