Setting a single locale for GWT application

One library used to output messages in German when locale was not set explicitly (<extend-property name="locale" values="en"/>). After we add an English locale to GWT module compilation began to take twice more time than in was before and the count of compilation permutations grew twice time too. It appeared that we cannot just user . Compilation was just failing with that. After googling a bit I've found a strange example which was promised to work. And it did worked! :) So, here it is:

<extend-property name='locale' values='en'/>
<set-property-fallback name='locale' value='en'/>
<set-property name='locale' value='en'/>

Though it looks like a hack (and in fact it really is), but it do work! Now our project has single English locale and compiles in 6 permutations.