How to detect the System Language on the destination PC?

Use the SystemLanguageID property.

In the WSI package:

Go to the Setup Editor view:

-Click the Product tab

-Go to Launch Conditions

-In right panel, right-click New -> Launch Conditions

-Click Build button

-Enter SystemLanguageID = 1033 (1033 is English_United_States)

-Click Paste and Ok

-In message text:

This package was designed to install only on system of a specific Language. Contact your administrator.

-Click Ok