FEAT #11269 TIME 0:20 add var lang

src/frontend/app/indexation/indexation.component.html

...app/indexation/indexing-form/indexing-form.component.html

...d/app/indexation/indexing-form/indexing-form.component.ts

src/frontend/lang/lang-en.ts

src/frontend/lang/lang-fr.ts

src/frontend/lang/lang-nl.ts