If I understand correctly, this is a follow up to T185761.
There are many message keys in WikibaseLexeme that begin with "wikibaselexeme-api-error-*". If these are apierror messages, they must begin with "apierror-wikibaselexeme-", according to https://www.mediawiki.org/wiki/API:Localisation .
It looks like there are 18 messages to update:
"wikibaselexeme-api-error-parameter-required": "Parameter \"$1\" is required", "wikibaselexeme-api-error-parameter-invalid-json-object": "Parameter \"$1\" expected to be a valid JSON object, given \"$2\"", "wikibaselexeme-api-error-lexeme-not-found": "Field \"$1\" contains an ID of a Lexeme \"$2\" that could not be found.", "wikibaselexeme-api-error-form-not-found": "Field \"$1\" contains an ID of a Form \"$2\" that could not be found.", "wikibaselexeme-api-error-sense-not-found": "Field \"$1\" contains an ID of a Sense \"$2\" that could not be found.", "wikibaselexeme-api-error-json-field-required": "Field \"$3\" at \"$2\" in parameter \"$1\" is required", "wikibaselexeme-api-error-json-field-not-item-id": "Field \"$2\" in parameter \"$1\" expected to be na Item Id. Given: \"$3\"", "wikibaselexeme-api-error-json-field-has-wrong-type": "Field \"$2\" in parameter \"$1\" expected to be of type \"$3\". Given: \"$4\"", "wikibaselexeme-api-error-parameter-not-lexeme-id": "Parameter \"$1\" expected to be a Lexeme ID. Given: \"$2\"", "wikibaselexeme-api-error-parameter-not-form-id": "Field \"$2\" in parameter \"$1\" expected to be a Form ID. Given: \"$3\"", "wikibaselexeme-api-error-parameter-not-sense-id": "Field \"$2\" in parameter \"$1\" expected to be a Sense ID. Given: \"$3\"", "wikibaselexeme-api-error-lexeme-term-text-cannot-be-empty": "Term text cannot be empty", "wikibaselexeme-api-error-lexeme-term-language-cannot-be-empty": "Language cannot be empty", "wikibaselexeme-api-error-language-inconsistent": "Language in field \"$1\" at \"$2\" was expected to be \"$3\". Given: \"$4\"", "wikibaselexeme-api-error-form-must-have-at-least-one-representation": "Form must have at least one representation", "wikibaselexeme-api-error-sense-must-have-at-least-one-gloss": "Sense must have at least one gloss", "wikibaselexeme-api-error-unknown-language": "Unknown language \"$3\" in field \"$1\" at \"$2\".", "wikibaselexeme-api-error-invalid-item-id": "Invalid item id \"$3\" in field \"$1\" at \"$2\".",