Just want to clarify again, my attempt at a language was meant to be for a tiny tiny group, so I apologize if my gaelic celtic thing threw anyone off

As for the Minmatar under the occupation of the Amarr, I don't think its so much a mix of both as first one, then the other. The timeline says that raids were conducted for 125 years. So, Gotti's analogy with Western Africa. Most likely the Amarrians would destroy any space or military infrastructure it encountered at this time, take the number of people they wanted and leave, wash, rinse, repeat.
Then, in 22480 Matar was conquered, but other Minmatar planets are left alone. This sounds like they are not trying to rip apart any remaining infrastructure, but rather funnel it to their own ends, much like the British Empire in India, or Hong Kong. This analogy also fits well to what the ratio of Minmatar to Amarr would have been on Minmatar worlds at this time. While conquering these people could be done, wiping out the major languages and culture shared across planets would next to impossible.
By 22947 they have occupied Starkman Prime for at least a generation. Whatever planets that are left to be conquered are probably not large ones, and most likely not habitable, being mining colonies, or even just stations. In a context like this, banning certain practises like tattooing might indeed make them come to be forgotten (Since the Nefantar would have given it up freely). It is probably not the only part of their culture that got tweaked, but in the end, its hardly enough to completely destroy a culture of what is likely to be at the bare minimum three or four billions of people, even over the course of hundreds of years.
Any slaves transported back to empire would of course lose touch with their roots and language, and here I think it goes back to Gotti's analogy again, further extended. There would probably be Minmatar patois' local to different Amarrian Holdings.
Think the PF is just fine *shrugs*