fix: add documentation for using chartoptions to set language translations

[sujoykd]

fix for #4690

[CLAassistant]

All committers have signed the CLA.

[github-actions]

AI Language Review

The new section added at the end of the file under == Chart Language is an essential addition for localizing charts. However, it would be helpful to include a brief explanation or introduction before this code section to guide the reader. This introduction can explain the purpose of localization and how the Lang class is used to achieve it in Vaadin charts. Otherwise, the content is well-written and clear.