Relationships between Finland and Sweden would be quiet cold during next decades. And hardly relationships between Finnish and Swedish speakers in Finland would be very good, not that these would had beeen great anyway but things might become nastier.
This could well lead into more and deeper language strife in Finland in the 20s and 30s. And then if the Swedish government somehow decides it should become the defender of the rights of the Swedish-speakers in Finland... Then it all could mean some real trouble diplomatically between Finland and Sweden.
I guess circumstances could conspire to turn this situation into one where the Finnish nationalist right is boosted in such a manner that, with the moderates divided about the language issue, the far right manages to take power and turn Finland into a semi-authoritarian state like many other new post-WWI nations between Germany and the USSR. Things were touch and go for a time in the early 30s in Finland, and this might be the thing that breaks the camel's back. That, IMO, might be the worst the butterflies could bring in this situation.
Come the late 30s, this all would mean that Sweden would be in an ironic situation in comparison to the OTL: in terms of having the Ålands, that is now threatened by the Soviets and maybe the Germans if war breaks out, they would have an interest to work with the Finns to protect the islands. But it would be a more unsavoury Finland than IOTL, one that would be very suspicious towards Sweden, though of course even more opposed to the Soviets, comparatively, than IOTL. And this right-wing, less democratic Finland, with its more open hostility towards the USSR, would from Stockholm's POV only serve to further destabilize the northern Baltic Sea area.
At end of this, we could see Finland occupied by the USSR, maybe becoming an SSR and Sweden standing a comparatively bigger chance to be drawn into the Second World War than IOTL.