[NOREF] Discussions translation fixes

[aterstriep]

NOREF

Description

• Added the discussions translation file to src/i18n/en-US/index.ts
• Updated translations to use count variable name and use singular/plural language (ex: 1 reply vs 2 replies)
  • Docs on i18next plurals
• Fixed typos

How to test this change

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• I have provided a detailed description of the changes in this PR.
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• I have updated tests or written new tests as appropriate in this PR.

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