Vue sample app - set i18n initial language based on SSR language or s…

[kbauer-hhog]

Description

Vue sample - Set i18n initial language based on SSR language or static config defaultLanguage to prevent re-renders in multi-lingual apps during the hydration process. (Same fix as #330, but for Vue sample app)

Motivation

To fix the flicker after initial page load issue when using the Vue sample.

How Has This Been Tested?

I have tested local Sitecore 9.3 instance with a JSS 13.0 site and debug via chrome dev tools.
My change simply initializes the language for i18ninit by pulling the SSR language from JSS_STATE, or using the config defaultLanguage setting.
The comments in code seem to support this, but I feel this could be introduced to prevent others from experiencing this issue OOTB.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have read the Contributing guide.
• My code follows the code style of this project.
• My change requires a change to the documentation.