Seems harmless to me, it's not as tho he JUST talked to him Klingon and set him up to not fit in. If anything it seems probably good for language skills to be exposed to more than one.
Altho I guess it's kind of weird and maybe even a little detached to not speak in the language that comes most natural to him, it's like he's putting the experiment above genuine communication with his baby. But it depends how natural he felt speaking Klingon I guess.
RE: TIL A Man Spoke Only Klingon To His Baby Son