The bug

Very high (and very low) levels of effects and enchantments display the following:

• For effects (levels 7 to 127, no negatives), it will display potion.potency.<level>
• For enchantments (levels 11 to 32767, levels -1 to -32768), it will display enchantment.level.<level>

Fixes

• Version 1.12 and below: en_us.lang
• Version 1.13 and above: en_us.json

  Side note

  Because I cannot find letters with a vinculum on top of them to represent higher Roman numerals, I used basic mathematical operations instead.

Notes

I am aware that this bug has a high chance to be resolved as 'Invalid' but please reconsider now that there are fixes made (albeit fixes that are quite large in terms of computer memory).