Speech Impediments - For When PCs Remember a Language They've Never Spoken

We've all been there.

The party is confronted with an otherworldly horror uttering guttural chants, or behold a mysterious elven monolith covered in curling runes that twist before their eyes, or stand enraptured before the song of an ancient angel from a forgotten heaven, or receive an email from the marketing department.

Then one of your players hits you with the "oh wait that's one of my languages!" and you have to let them speak to whatever it is.

In regular D&D where you pick Languages during char gen, this happens when it turns out someone has been able to speak Gnomish or Celestial the whole time.

In my game this happens because my players insist on rolling Languages any time they come across a new creature that shows even the tiniest glimmer of sentience. This is why several characters apparently speak fluent Eastern Lowland Gorillese.
This is really very silly but it's fun enough to keep (a la the secret fourth option in this post).

What's the "solution" to this "problem"?
They obviously know the language, but given the fact that they've never even mentioned that they can speak it in months of adventuring it must have been quite a while since they did that exchange trip to the eighth circle of hell.
But they're totally fluent of course, but uhhh... how do you say...

I'm a Bit Rusty

The first time your character speaks a language that they haven't previously spoken in-game, they're rusty.

Roll 1d30:

Roll	Result
1	Can only speak in single syllables
2	Tourist phrasebook content only - "two beers please", "which way to museum?" etc.
3	They understand you but are always offended.
4	Words that start with a vowel only.
5	One word sentences only.
6	Absolutely always alliterate.
7	Words that start with a plosive only
8	Must "speak" by describing emojis.
9	Swear words only.
10	Must speak way too loudly.
11	Can only speak in quotations and metaphor.
12	Sentences must be spoken in reverse order
13	"Snake Snanguage" - all words start with the first two sounds of that language.
14	Unable to use pronouns (I/you/he/her/it/etc)
15	Unable to speak in present tense
16	No verbs
17	Speak in Haiku
18	Can only write it, not speak it.
19	Only know numbers
20	"G" and "J" must be pronounced with a soft "zh" sound, as in treasure or casual
21	No nouns
22	Last letter of one word must begin the next word.
23	One must refer to oneself as one, and instead of "we" or "they" must state the number of people in the group (eg. "One was with Four when someone robbed Two house")
24	No adjectives
25	All phrases must be an innuendo, if you know what I mean
26	All sentences must be noun-verb-object
27	Must stand on one leg while speaking
28	Overly formal, everyone must have a title, no contractions, etc etc
29	Every noun must be described by an incongruous and/or false adjective.
30	Can speak the language but only in a cartoonish over the top accent.

When you speak that language you must abide by the rolled limitation.
This represents your character pausing to think, forgetting words, getting tones wrong, using the wrong conjugations, and other such issues with dredging up the language you haven't used in a long time.
Failing to do so means you've said complete gobbledegook and nobody understands what you just said.

In subsequent sessions it's all come back to you and you are completely fluent.
Presumably you quickly brushed up on some refresher notes, or beseeched the Horrible Green Owl to reinstate your streak.

Specialists, of course, are always fluent from the get-go. Skills are their whole deal after all.

Inspired by the meta-diseases over at Beneath Foreign Planets.