If I don't use Polylang Pro, slugs can't be reused. What does that mean?

In WordPress, category and tag slugs must be unique in the database across the whole site—not per language. So you cannot keep the exact same slug for the English term and its Spanish translation when both would collide.

Example: You have the tag “banana” in English and the translation is also “banana” in Spanish. The English slug is banana. WordPress will not store a second term with slug banana, so Polylang will assign something like banana-2 for the Spanish tag.

Polylang Pro works around this with a feature that effectively “shares” slugs: it behaves as if the slug were banana-2, then rewrites the SQL right before the row is saved so the database ends up with banana anyway. It is a bit of a hack, but it is the established way to get identical slugs where WordPress would normally forbid it.

So:

• If you need the same slug in every language (clean URLs, SEO expectations, consistency), you need Polylang Pro (or another approach that solves the same constraint).
• If you are fine with occasional suffixes like -2, the free version is enough.

How often does -2 actually show up? Often only when the translated name would produce the same slug as the original—e.g. cognates like “banana” → “banana”. If English is “apple” and Spanish is “manzana”, the slugs are apple and manzana, so there is no collision.

Practical approach: Start with Polylang free, see how many terms end up with -2. If you later move to Pro, you can manually edit those few slugs; there are usually only a handful.