Do you think is necessary to create an auxiliary translate table for table that has only two elements (id and name)
Definitely the first one with both Allergen and AllergenTranslation tables.

The reason is that Allergen is likely to be referenced in other places. Say you have a table of medicines each of which is effective against a subset of allergens. What would be the foreign key in this Efficacy table? You don't want that FK to have LanguageId in it at all - the medicine's response is not conditional on the patient's speech. Nor do you want to repeat rows in Efficacy for each language as this is redundancy leading to duplication and errors. Think of the changes required to introduce another language.