My favorite way to look up old town names and variations is through the JewishGen.org website. It's not 100% complete, but it's pretty great, and you can do sorting on county, provincial, and/or national borders in the pre-WWI, Interwar, and/or post-WWII periods.
That said, there are a lot of town names in the pre-WWI Russian Empire lands that might be "Salash". One fair possibility is Selishche, in what was then Kishinev, Bessarabia, Russian Empire -- today it's Seliştea Nouă, Moldova -- but there were many possibilities if you do a search there.
Another good possibility: Selets, Pruzhany, Grodno gubernia (province), Russian Empire -- today it's Syalyets, Belarus.