Based on the recipient data, you can, in one message, create different content for your recipients.
E.g. if you want to send one email to recipients that have different languages you can use the switch function:
{{#switch contact.language}}{{#compare "==" 'fr'}}French sentence.{{/compare}}{{#compare "==" 'sv'}}Swedish sentence.{{/compare}}{{#default}}English sentence.{{/default}}{{/switch}}
You can add it like any other text to your message content, subject line, pre-header or dynamic web page.
All recipients that have the attribute value fr will get the French sentence, all with the attribute value sv will get the Swedish sentence and all others, with no or a different attribute value than fr and sv will get the English sentence.
If it becomes too long and disturbs your layout overview, you can use Snippets. Add the function there and the snippet handlebar in the message. The disadvantage is that there will be a lot of snippets if you use several for every message.
Another possibility is to use Segments, e.g. if it is easier for you to create content blocks in different languages and add the right segment to each block.
The attribute name can of course be any other than language and you can use the switch function for any other conditional content. See more examples at the Handlebars rundown page.