I think that this suggestion runs counter to the intention of the OP. I believe that we're looking for reasons to not dump intelligence, rather than specifically rewarding wizards for maxing it out.
Your suggestion would reduce the range of skills a character has unless they roll up ability scores, get lucky, and put their highest score into intelligence. There is no reward for having anything less than a 16 in Int, and even with that the character would be losing versatility compared to the usual way of character generation.
I think that we're after reasons to put a 12, 13, or 14 in Int rather than dumping it. The general consensus seems to be that Wizards are the only people likely to be maxing it out, and that they don't need much extra power.
We could simply take out the -2 skills to start, and say that a -1 Int loses one skill, but +X Int gains X skills.
Skills. Your total number of skill proficiencies equals your Race Skills + Class Skills + Background Skills + Intelligence Modifier. If your Intelligence modifier decreases during your adventure, you do not lose skill proficiencies. Your skill proficiencies must be chosen from your race, background, and class lists.
A player will only not dump a stat if that stat is necessary to a decent build. You have to penalize negative Int like you do negative Dex or anything else. Because Int is used for fewer checks, attacks, saves, damage, etc, it is easily dumped. Fixing this requires making Int valuable. Linking Int to skill-learning ability would meet this goal.
My proposed change takes equally from all classes, but it would give Wizards a bonus because they use Int naturally. But Wizards already suffer from dumping other stats.
Granting language and tool proficiencies will not be effective in curbing Int dumps. Languages are already readily available, and in many games they aren't very necessary. Likewise, almost all tools are usually of limited use. If Xanathar's makes tools more useful, that would be great, but in the meantime, they are ribbon features, and a ribbon does little to discourage stat dumping.
What really needs to happen is for spells to be re-written to give many more Int and Cha saves.