the only place where a European language fully diverged from the tongue spoken in the motherland was with Afrikaans in South Africa.
Is Afrikaans really another language?. I don't speak Dutch either but transcriptions of both languages are essentially the same thing as far as I have seen.
It seems to me that why it is considered a different language while say Ebonics, Gaelic dialects of English, Coast English(West African Pidgin) and Hong Kong Pidgin aren't even tho it is harder for a English man to understand either of those than it is for a Dutch to understand Afrikaans is because of the usual, "A language is a tongue with a state and army", South Africa is a different state, didn't get it's independence from the Dutch but from Britain through a process where the Dutch colonizers developed an identity distinct from the colonial states. It is the same reason Quebecoise, Cajun and Arcadian are treated as different languages sometimes.(Tho wait, the French dialects in North North America don't seem to be considered different languages so, my mistake).
There's also that again Cajuns and Afrikaans and coloureds recognize themselves as Cajuns and Afrikaner while an Igbo speaking Pidgin doesn't recognize themselves as a Pidginese. This second reason is probably why the various creole languages exist and are recognized as different languages because Haitians, Krios and Jamaicans exist. I don't really know how much these diverge from their base language but I assume way more than Afrikaans diverges from current or period Dutch. So unlike Afrikaans I'll probably consider alot of them, actually different languages tho not the ones that I have heard and understand, Liberal English/Creole and Krio(Sierre Leone English Creole) certainly is just a dialect of English by intelligibly, like Krio is just Coast English so that's it in OTL for one coast English timeline.
So you want to make more colonial languages, make those two stuff a reality. You don't even necessarily need colonization, Coast English was spoken across the Atlantic coast of Africa, if some coastal power to unifies that coast and then expand inland the language of the identity and the people that make up the core of that Empire will probably be Coast English.
Maybe if essentially every colony has been colonized two times over, like Dutch and Swedish populations established in Nee York and neighbouring areas before the British take it over, and it has to be before cuz later large migrant communities tend to be recorded as a dialect than as a language of its own like Texan German and the Amish varieties of German.
So maybe if Britain actually colonized recently independent Spanish Americas and the Dutch succeed in Brazil and the Kongolese succeed in Angola, you get different Hispanic and Lusophone languages.
Anyways for something that I actually consider a different language squarely and is also recognized as such, there's Tok Pisin of Papua, it emerged from English.