M Owen
Welcome to the site. From what I have read, early recruits in Rimington's Guides, at around the commencement of hostilities with the Boers, would have needed some familiarity with Afrikaans due to their intended employment. At that point, RG was a relatively small unit. Albeit a crack one. Later, during the campaign, the unit became known as Damant's Horse - much to the chagrin of it's original members. I would suggest that the need for Afrikaans speakers later in the campaign would not have been as acute as at the commencement.
The nominal roll images on this site show that "35801 Pte. John Roche" on the Damant's Horse roll served from 29/7/01 to 31/1/02 and earned the clasps Cape Colony, Orange Free State, Transvaal, South Africa 1901 and South Africa 1902 on his QSA medal. The medal was issued 2/6/04. His entry on the medal rolls (WO100/ 244) shows the marginal note "5th Irish Volunteers". That could mean previous service at home in the Volunteers.
I am sure that your GU saw some exciting times during his service with Damant's Horse. The unit history on this site should give you some of the bare bones of his service.
Regards
IL.