By default, Option Price Calculator uses English language for error messages displayed in Option Price Calculator.
These messages can be changed here:
Settings -> Miscellaneous Config -> Translations

Multi-select field errors
– Must select at least
– Must select exactly
– Must select between
General Errors
– Required fields missing
– Product not available
– all remaining stock is in your cart
Lookup Errors
– The minimum for
– The maximum for
– decimal points allowed
Misc words
– is
– and
– Only