Dutch, Portuguese, French Website Translation

I already have an website with some languages translation, but I want to add this 3 languages more.

I need my entire website—every page, post, menu, and tiny footer note—available in Dutch, Portuguese, and French. Once the translations are in place, visitors must be able to switch languages from a clear drop-down in the top navigation bar.

Here’s what success looks like for me:
• A complete, accurate translation of all existing content (no machine-only output; final copy must read naturally to native speakers).
• The language menu added to the main nav and visible on every page.
• URLs, meta titles, and descriptions mirrored in each language so search engines index them correctly.
• A short hand-off guide explaining how I can add or edit translated content later.

You’ll receive full admin access to implement everything. Let me know the tools or plugins you prefer—WPML, Polylang, custom code, or another method—and your estimated timeline.