[r-s]

I generally do internationalize apps that I build right from the start. The cost for switching at a later date I have found to be very significant.

I do not however localize them until its needed. Often working with translators and ensuring the quality of the localized application is not a huge priority in the beginning.

[brlewis]

I believe you, but my experience is different. IME i18n and l10n are a lot of work even if you plan on them from the beginning. For projects I've worked on it wouldn't save that much effort to architect for i18n up front. I would go with just one language until product-market fit, then assess whether it's worth internationalizing/localizing.