Hi,

First make sure that the intended field is translatable field in Odoo, if yes, you can do as follows, activate all 3 languages in odoo, you can activate different language from the language menu in the settings.

Once the language is activated, import the english description first. Keep the external id of the products in the sheet, so that it can be used in further imports. Once english is imported, switch the odoo language to the next language and import the description in that language to the same record and similarly do for the third language also.

Thanks