What is the scottish Gaelic for happy wedding anniversary?

In Irish:

Comhgáirdeas bhur gceiliúradh (plural)

Comhgáirdeas do cheiliúradh (singular)

In Scottish Gaelic: Cuirm Bhliadhnail Sona

Be aware that 'Gaelic' is actually two separate languages: Scottish Gaelic (called 'Gaelic' in Scotland) and Irish Gaelic (called 'Irish' in Ireland).