"I am James"
Translation:Is mise Seumas
You certainly could. In the Gàidhealtachd, people will often have their given name and then the English one they go by. For example, you may meet someone who introduces themselves as Iain Fionnlagh if they know you have the Gàidhlig but as Ian or John Finlay otherwise. I personally haven't seen it so much in the Highlands but I've certainly experienced it in the Islands. A dive into the history in the Gàidhealtachd would be necessary to go in depth as to why they may choose one with their family and friends and an English version for the rest of the world.
It's covered in the course notes under, "Is mise Duo" and "Emphatic Pronouns".
Formally, there's an entire grammar around using the copula and equating things but the short answer is that you define yourself with "is mise", you describe yourself with "tha mi".