Twitter's code is "enterprise" code in that it has to satisfy the organization's needs and a huge part of it is not user-facing, but targeting other enterprises (for example, Twitter ads). At Twitter, we use Scala.

So, no, you're not necessarily stuck between these two options (or Java, which is another popular choice in the enterprise scene). Scala was chosen specifically, among other things, because Twitter had a lot of Ruby developers who would cringe at the idea of PHP, Java, or .NET.