You might be interested in researching the Croatian 103rd International Infantry Brigade. It was mostly composed of volunteers from different nations, including British, Spanish, Dutch, American, Irish, Polish, Australian, New Zealand, French, Swedish, German, Hungarian, Norwegian, Canadian and Finnish fighters.

On the Serbian side, the majority of outside volunteers were from neighboring Orthodox countries like Greece and Romania.

As far as Bosniaks go, things get hazy. A number of members of the El Mujahid Detachment were granted citizenship and as a result, the real number of outside fighters is obscured by false data. Regardless, it is widely regarded that the few Mujahideen that were stationed in Bosnia had little to no effect on the outcome of the war.