Note that Latin is generally considered to have about four irregular verbs, possibly a few more than that depending on how you're counting.
A verb in Ancient Greek has six principal parts, which means that to correctly inflect it you need to memorize six more-or-less independent forms.† (They're often "less" independent, but sometimes they'll surprise you!)
By contrast, an English verb, except for the single verb be, has a maximum of five forms. (Not five principal parts - five fully-inflected forms!) So by the Greek standard, English has just the one irregular verb. That's not a correct application of the concept, but it is worth observing.
> I don't think French has examples as crazy as go -> went. I mean, there aren't even letters in common!
This is a suppletive verb. (That is, a verb in which some forms descend from one ancestral verb and other forms descend from a different ancestral verb.‡) Went was originally the past tense of the still-existent verb wend, in the same way that bent is still today the past tense of bend; wend has had to shift over to wended.
Not only does French have suppletive verbs, it has the same suppletive verb, aller [to go]:
1sg pres. je vais [< Lat. vadere]
1sg impf. j'allais [< Lat. alare]
1sg fut. j'irai [< Lat. ire]
The Latin verb is ire; it is minorly irregular but not suppletive in Latin. Suppletion is present in Latin anyway; the best-known example would be fero, whose third principle part tuli is taken from tollo. In turn, tollo uses sustuli [= sub- + tuli] as its third principal part, and then sustuli is left ambiguous between being the perfect form of tollo or of suffero [= sub- + fero].
Circling back around, we can note that while fero is one of the rare Latin verbs that comes with a warning that its conjugation is irregular, that's not because its perfect forms are taken from an unrelated verb. By itself, that would barely be worth remarking on.
† And this is a convenience for modern students. Actual speakers of the language would have thought about their verbs a bit differently - in a number of common cases, one of the principal parts is a form that doesn't otherwise exist in the language, which native speakers would never have considered.
‡ Suppletion as a linguistic phenomenon is not restricted to verbs; compare person -> people.
Note that Latin is generally considered to have about four irregular verbs, possibly a few more than that depending on how you're counting.
A verb in Ancient Greek has six principal parts, which means that to correctly inflect it you need to memorize six more-or-less independent forms.† (They're often "less" independent, but sometimes they'll surprise you!)
By contrast, an English verb, except for the single verb be, has a maximum of five forms. (Not five principal parts - five fully-inflected forms!) So by the Greek standard, English has just the one irregular verb. That's not a correct application of the concept, but it is worth observing.
> I don't think French has examples as crazy as go -> went. I mean, there aren't even letters in common!
This is a suppletive verb. (That is, a verb in which some forms descend from one ancestral verb and other forms descend from a different ancestral verb.‡) Went was originally the past tense of the still-existent verb wend, in the same way that bent is still today the past tense of bend; wend has had to shift over to wended.
Not only does French have suppletive verbs, it has the same suppletive verb, aller [to go]:
The Latin verb is ire; it is minorly irregular but not suppletive in Latin. Suppletion is present in Latin anyway; the best-known example would be fero, whose third principle part tuli is taken from tollo. In turn, tollo uses sustuli [= sub- + tuli] as its third principal part, and then sustuli is left ambiguous between being the perfect form of tollo or of suffero [= sub- + fero].Circling back around, we can note that while fero is one of the rare Latin verbs that comes with a warning that its conjugation is irregular, that's not because its perfect forms are taken from an unrelated verb. By itself, that would barely be worth remarking on.
† And this is a convenience for modern students. Actual speakers of the language would have thought about their verbs a bit differently - in a number of common cases, one of the principal parts is a form that doesn't otherwise exist in the language, which native speakers would never have considered.
‡ Suppletion as a linguistic phenomenon is not restricted to verbs; compare person -> people.