"gd" and "ga", or "gla" and "gld"

[Caoimhin O Donnaile]

I have been thinking that the time has possibly come to give
language labels to the many thousands of pages on our Gaelic college
website.  But should I use:

   <meta http-equiv="Content-Language" content="gd">
and:
   <meta http-equiv="Content-Language" content="ga">

for Scottish and Irish Gaelic respectively, or should I use the
three-letter codes

   <meta http-equiv="Content-Language" content="gla">
and:
   <meta http-equiv="Content-Language" content="gle">

I seem to remember a rule saying that two-letter codes should be used
if these are available, but my tidy mind would prefer three-letter codes
for all languages, and I have a feeling that these might be on the
way with the unification between Ethnologue codes and ISO 639-2.

(Actually I would have preferred four-letter codes for languages
and three-letter codes for scripts, but I guess it is a bit late
for that idea?)

Caoimhín