You only need to apply the latest non-language and language dependent fixes. Since March did not have a language-dependent fix, you will need to apply the Feb 2019 language-dependent fix.
You can check the KB of the CU to check if it includes all previous Cumulative updates and security updates like this.
If it contains, you will see like the below:
But, if you install a CU after SP1 for SharePoint 2013, you need to make sure you have installed SP1 which is a prerequisites.
CU includes security updates and every other update from previous months. So there is no need to install a SU separately after installing and applying a CU for the same month. (if not stated otherwise by MS).
It seems that this is an ongoing "bug" with IE updates as there is a workaround mentioned the following two KB articles for IE Security Updates:
Cumulative security update for Internet Explorer: March 12, 2019
Cumulative security update for Internet Explorer: April 9, 2019