What do you mean 'wrong'? They're pronounced the way the language is pronounced, and represent the phonemes they're associated with. All languages do that.

For example, the ll digraph in English, Icelandic, Welsh, and Catalan is pronounced differently in each language. In English, it's got the same value as a single l, in Icelandic it's got the value of either [tɬ] or [tl] depending on context, in Welsh it's got the value of ɬ, and in Catalan it's /ʎ/. Each is correct in their respective language.

Adoption of the Latin alphabet generally went hand in hand with adoption of Christianity and the associated literary culture.

The only Irish writing before Latin script was Ogham, which as far as we can tell was mostly/only used in inscriptions.

Originally, languages adopting the Latin script used spelling systems that were quite regular, and were pronounced as you might expect if you know what sounds Latin letters have in most languages that use them.

Irish looks so weird (and it is weird, by the standards of most languages using the Latin alphabet) for two reasons. The first is that Old Irish had some phonological features that were difficult to represent with the Latin alphabet as they received it. The second is that Irish changed a lot, and applying and adapting the old spelling rules to the new language led to even more spelling practices unique to Irish.

The same kind of thing happened to every other written language over the same time period, but because of orthography reform and the nature of their particular changes, few today have systems that are as weird as Irish. English is a notable exception - our unique spelling rules and exceptions outnumber even those of Irish.

Follow up question: I know in modern times there are examples of languages without writing adopting other alphabets and consciously deciding to use letters in a certain way (the example I'm familiar with is Wolof using "X" to make the same sound as the Hebrew "ch", ie the "clearing your throat sound.") Are there any examples in history of this sort of top down alphabet acquisition?