Add coach strings

[MisRob]

Summary

Prepares strings for issue #9849

Reviewer guidance

Please see the acceptance criteria of #9849 and linked Figma designs and check that all strings needed are here.

Testing checklist

• Contributor has fully tested the PR manually
• If there are any front-end changes, before/after screenshots are included
• Critical user journeys are covered by Gherkin stories
• Critical and brittle code paths are covered by unit tests

PR process

• PR has the correct target branch and milestone
• PR has 'needs review' or 'work-in-progress' label
• If PR is ready for review, a reviewer has been added. (Don't use 'Assignees')
• If this is an important user-facing change, PR or related issue has a 'changelog' label
• If this includes an internal dependency change, a link to the diff is provided

Reviewer checklist

• Automated test coverage is satisfactory
• PR is fully functional
• PR has been tested for accessibility regressions
• External dependency files were updated if necessary (yarn and pip)
• Documentation is updated
• Contributor is in AUTHORS.md

[github-actions]

Build Artifacts

Asset type	Download link
PEX file	kolibri-0.16.0a7.dev0_git.131.g010dc310.pex
Windows Installer (EXE)	kolibri-0.16.0a7.dev0+git.131.g010dc310-unsigned.exe
Debian Package	kolibri_0.16.0a7.dev0+git.131.g010dc310-0ubuntu1_all.deb
Mac Installer (DMG)	kolibri-0.16.0a7.dev0+git.131.g010dc310-0.3.0.dmg
Source Tarball	kolibri-0.16.0a7.dev0+git.131.g010dc310.tar.gz
WHL file	kolibri-0.16.0a7.dev0+git.131.g010dc310-py2.py3-none-any.whl

[radinamatic]

Slight context rewording necessary, but can be merged afterwards 👍🏽

[MisRob]

Thank you @radinamatic, done