Why doesn't this Google Translate ad use the word "Translation" instead of "Translate"?

Solution 1:

"Translate" here refers to the name of the product: Google Translate. This makes it a noun-adjunct, I believe. You can see them use the full name elsewhere, when they have more room (emphasis added):

Help improve Google Translate

You can help make our translations better, and even add new languages, as part of the Google Translate Community.

Solution 2:

Although Laurel's answer has been accepted, I'd like to take a different angle.

The banner on Google's site reads:

JOIN THE TRANSLATE COMMUNITY

Because the banner is on Google's own site it would stand to reason they're talking about their own product. Thus, you can drop the "Google" in Google translate as a way of contraction. You'd still be able to recognize the "Translate" as a product name because it's a proper noun, capitalizing the first letter. The confusion stems from the sentence being all uppercase.

If the sentence wasn't all capitals, the intent would be much clearer: