To describe a person "fond of ... Celtic culture or languages", two choices exist, less and more extreme:
Celtophil n. a friend of the Celts and Celtic studies.
Celtomaniac n. one who is crazy on Celtic matters; esp. one who pretends to derive all languages from Celtic.
["Celto-, comb. form". OED Online. September 2016. Oxford University Press. http://www.oed.com/view/Entry/29542?rskey=2qqCFS&result=31&isAdvanced=false (accessed October 19, 2016).]
As shown in the citation provided by the OED, both these words are found as subentries of the main 'Celto-' combining form entry; they are not, however, listed as nonce-words. Any lexical nonceness, such as it might be, would therefore derive from the words being instances of the combining form in use.
To describe a person "fond of Irish ... culture or languages", OED Online does not list any word, from the combining 'Hiberno-' or otherwise derived. OED Online does list 'Hibernophobe' as a nonce-word:
One who has a dread of or antipathy to the Irish.
"Hibernophobe, n.". OED Online. September 2016. Oxford University Press. http://www.oed.com/view/Entry/86675?rskey=qVLlMh&result=26&isAdvanced=false (accessed October 19, 2016).
In addition, and supplementing the evidence, provided by the listing of 'Hibernophobe' with no corresponding listing of 'Hibernophil', of a deep-seated if not systemic prejudice against the Irish embedded in the British language and literature, OED Online gives the following definition of 'Irishism':
1. A statement which is manifestly self-contradictory or inconsistent.
"Irishism, n.". OED Online. September 2016. Oxford University Press. http://www.oed.com/view/Entry/99476?redirectedFrom=Irishism (accessed October 19, 2016).
It's true and possibly extenuating that the later use of 'Irishism' is more temperate and impartial:
2. A characteristically Irish word, phrase, or idiom. Also occas. more generally: a characteristically Irish belief, attitude, or trait.
Any recovery from the bias expressed by the first and earlier meaning evidenced by the second more impartial use, however, is undermined by another, and later, trend in the use of 'Irishism':
3. Chiefly depreciative. The fact or quality of being Irish; Irishness.