ISO keycaps refer to keycap sets designed according to the International Organization for Standardization's layout for keyboards, which includes specific characteristics like the shape of the "Enter" key and the placement of certain punctuation symbols. The language options, such as ISO-DE for German and ISO-FR for French, indicate the inclusion of language-specific characters (e.g., ä, ö, ü, ß for German, and é, à, ç, è for French) tailored to the typing needs of those language speakers. This design accommodates the unique alphabet and punctuation requirements of different languages within the standardized ISO layout framework.