It is not possible to change the language within one survey package. For these cases we recommend you to create separate surveys and survey packages for the different languages. Keep in mind that every question in the different languages will have their own variable name in the export file, as these need to be unique. However, if the questions, the order of the questions and the number of the questions are exactly the same throughout the surveys, it should be possible to merge the datasets easily.
Alternatively, it is possible to create dependent fields based on the question in which the participant defines his preferred language. Keep in mind that also in this case the questions in all languages have their own unique variable name.