I'd like to ask gather some pros and cons about multilingual sites in Umbraco.

I'd like to know what issues you've faced, for example, did you have issues with searching? How was your site structured? What was your "Oh God. I've created a monster..." moment?

Multi-Tenant Site / Single Language;

Content
    MySite.com (Default language - English)
        - News
        - Products
        - Services
        - Contact Us
    MySite.NL  (Default language – Dutch)
        - Nieuws
        - Producten
        - Diensten
        - Contacteer ons

VS

Single Site / Multiple Language (using Vorto or similar)

Content
    MySite.com (Default language - English, Alternate Languages - French, Dutch, Spanish)
        - News
        - Products
        - Services
        - Contact Us

What are the pros & cons for this either of these approaches?

What some good questions/issues to raise with the client to preempt which approach might be best ? e.g.

In the multi tenantancy example, Regional content editors are able to update different content on different domains. It might be the case that some English products won't be available in the Netherlands. Where as, in the single site, this may cause issues since the page would exist, but the product wouldn't be available.

Really, I'm interested in problems, practice and theory... not code.