Perhaps, but do you speak Welsh fluently?
Nope. But I've passed exams in Modern and Medieval Welsh, and a couple of other Celtic languages. I spent six months in Aberystwyth living with a Welsh speaking family in a Welsh only program for Celticists. I passed thanks to the kindness of Welsh speakers all over Wales who were incredibly patient with me, as well as kind. Several strangers I met on the train or at cafes and shops spent a great deal of time helping me cope with the basics of navigating, shopping, and not starving in Welsh.
The mutations in Welsh are less of an issue for me than the VSO structure of Welsh, a characteristic it shares with all the Celtic languages, and which sometimes has me feeling like I'm speaking or writing backwards.
In broad terms, the Celtic languages changed very little (leaving aside the somewhat artificial aspects of Modern Irish as she is taught, vs Irish in the Gaeltacht) in comparison with the changes in English from Old English to Middle English, never mind Middle English to Modern.
A native speaker or someone fairly fluent in Modern Welsh can read Welsh from the 10th century on fairly easily; it's more like a native English speaker reading Shakespeare than reading Chaucer.
A native English speaker can't read the English of the tenth century without considerable study. It's too different. It's difficult to read even non-Chaucerian English of the 14th century. Welsh stabilized fairly early in comparison to English.
English isn't sensible. Look at tough, bough, and slough. Three different pronunciations. There's nothing about the three words themselves as they stand to explain the differentiation. Once you learn Welsh phonology, it's pretty consistent, though it differs a bit in terms of era and dialect, within an era or within a dialect, it's consistent.
Look at our To Be verb; it functions as both the substantive and the copula. Generally speaking, in I.E. languages they are two different verbs. In English, it's just one, with a bizarre phonology, because the various parts aren't actually related.
In English several verbs were hijacked and combined to create the full conjugation of To Be (Present tense
am and
is are cognate with Latin
sum and
est, and share the same Indo-European ancestor (es-).
Was and
were derive from an I.E. root meaning "remain" or "stay." The forms be and been are from a third verb, derived from the same I.E. root (
bheuə-) as Latin
fui “I was," and Latin
fio "I become." There's not a lot of agreement about where we got
are. Calvert Watkins thinks it's from er- but no one really has been get more definitive than that.
I think people who learn English as second or later language are incredible. I don't know that I'd be able to. Were it not my first language, I think the lack of consistency would cause me to despair.