You can!
Copy the en-US.xml file and rename it.
Edit the renamed file and read the manual.*
If you have finish, delete the en-US file (Copy it if you want)
and rename the file that has been modified to en-US.
Start Construct2 and it's OK!
<font color=red>*The party in italic is no obligatory if you have already downloaded an translation file</font>
I'm French: I speak English very bad, sorry