I found a fix for this…
In the FoF Linguist extension, click the Import tab and import the following:
foskym-custom-levels:
lib:
defaults:
tooltip: "[expTotal] Points."
or, for something more complex, you could use:
foskym-custom-levels:
admin:
settings:
expTooltip: Exp tooltip
expTooltipDesc: "Shown on hover. Variables: [expTotal], [expPercent], [nextLevel], [expToNextLevel]"
lib:
defaults:
tooltip: "[expTotal] XP · [expPercent]% toward next · [expToNextLevel] XP to level [nextLevel]"