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To keep track of the products in the different languages, the product feed needs to contain the information in all languages (of the domains). The fields that can differ on the basis of language are: name, url and description. You can find more information in this article under the heading 'Languages'.
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To keep track of the language of a profile, a custom profile field needs to be created (for example custom_language). In this field you keep track of the language in which the profile has seen the website for the last time. This value can then be sent in any event to update the field. More information on creating custom fields can be found here.
Keep in mind that the set up of your account is complicated
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