This is the technical support forum for WPML - the multilingual WordPress plugin.
This thread is resolved. Here is a description of the problem and solution.
Problem: WPMUDEV Domain Mapping not working with WPML.
Solution: The DOMAIN MAPPING plugin by 'wpmudev' is not in our compatibility list here https://wpml.org/documentation/plugins-compatibility/.
That said, it may not work as expected. If you set WPML Language settings to "Different languages in directories" then having the second languages load in subfolder such as rootdomain.com/site1 is expected.
If you want to use different languages per domain we recommend not using domain mapping and use the method outlined on this tutorial: https://wpml.org/2016/04/use-wpml-different-domains-per-language/
Relevant Documentation: https://wpml.org/2016/04/use-wpml-different-domains-per-language/