Take the name you want. Seriously. I do not know the name you have in mind.
Say you choose "Mark' If nothing is available that you like from the below list look at the ones closest. Then research that in the language you want, say Gaelic, Marcas (not listed below) Then find the alternate spellings. before standardized spellings certain languages (most) were all over the place with how stuff in spelled.
This was a very simple name. Take something like Oswald and you are off to the races....
In other languages
Belarusian: Марк
Bulgarian: Маркo, Марк
Breton: Mark
Catalan: Marc
Classical Syriac: ܡܪܩܘܣ
Coptic: Ⲙⲁⲣⲕⲟⲥ
Czech: Marek
Welsh: Marc
Danish: Mark
German: Markus, Marcus
Greek: Μάρκος
English: Mark, Marc, Marcus
Esperanto: Marko
Spanish: Marcos
Estonian: Markko
Basque: Marco
Finnish: Markku
French: Marc
Friulian: Marc
Lombard: March
Irish: Marc, Marcas
Croatian: Marko
Hungarian: Márk
Italian: Marco
Cornish: Margh
Latin: Marcus
Lithuanian: Markas
Latvian: Marks, Marcis, Mārcis, Mareks
Dutch: Mark
Norwegian: Markus
Polish: Marek
Portuguese: Marco, Marcos
Romanian: Marcu
Russian: Марк
Sardinian: Marcu
Slovak: Marek
Slovene: Marko
Serbian: Марко
Swedish: Mark, Markus
Turkish: Markos
Ukrainian: Марко, Марк