Ask user about language preference upon signup

**What problem are you trying to solve?**
User had Korean as an option in their browser language settings and when setting up MetaMask everything defaulted to Korean and it was difficult to find the settings to change it.

**Describe the solution you'd like**
upon signup ask the user what language they would use for default

**Additional context**
Add any other context or screenshots about the feature request here.

The issue names no files, tests, or entry points. Start by locating the signup flow and the existing browser-language and language-settings behavior described in the report. Define the preference prompt's place in setup and verify that a user's selected language becomes the default without making it difficult to change later.

Written by the indexing model from the issue text.