In the list of courses at the web site (https://www.memrise.com/courses/english/), the Galician language does not currently appear under the category “Languages: European”, but under the category “Languages: Other”.
I suggest Galician should be put into the category “Languages: European”.
Distinct language or mere dialect, the difference is imprecise and the definitions are not universal. Experts can debate for years and never reach a consensus. But the purpose of this thread is not to end a linguistic controversy, but to make it easier for users to find the Galician courses when browsing categories here.
If we consider Galician a distinct language, then it should definitely be in the “Languages: European” category rather than in “Languages: Other”.
If we consider Galician a mere dialect of Portuguese from a philological point of view, we may be tempted to simply remove the Galician category and include Galician courses in the Portuguese category. However, even if we were to assume this philological stance, we must take into account that: 1) a person proficient in standard Galician as currently taught in Galician schools but with no knowledge of standard Portuguese is unlikely to pass a Portuguese proficiency exam; 2) a person proficient in standard Portuguese but with no knowledge of standard Galician is unlikely to pass a Galician proficiency exam; 3) most users searching for Galician courses are unlikely to search for them in the Portuguese category. This may change in the future if proponents of Galician-Portuguese reunification eventually succeed, but in the present situation the differences between Galician and Portuguese, especially concerning vocabulary and orthography, are much bigger than those existing for example between American English and British English.
Therefore, regardless of one’s stance on whether Galician is a distinct language or just a Portuguese variant, I think that, from a practical educational point of view, Galician courses should be in their own language subcategory within the European language category.