The most expensive mistake is relying on the seller's lawyer. The developer is paid when the deal closes, which is a different interest than acting for you. Separate legal representation represents a fraction of what is at stake and is the single best safeguard.
Signing in a language you do not speak comes a close second. A certified translation is inexpensive compared with the sum being committed. Promises made buy land in egypt conversation will not help when the written text differs — the contract is what counts.
Buying off-plan without checking the developer has damaged plenty of plans. Before any payment, review the developer's completed projects, the building permits, and the guarantees on staged payments. Delays are normal even in good markets; abandoned sites are less common but much more damaging.
Forgetting about resale is a quieter mistake. A home bought abroad will eventually be sold, and the pool of future buyers determines the price. A property with no local demand is harder to move when conditions change.
Finally, a lot of buyers underestimate the ongoing obligations. Local tax returns are often required regardless of whether the samegrelo-upper svaneti property prices earns anything, and missed deadlines attract fines nobody warns you about. Putting in place a local tax adviser from the first year heads off most of it.