Usually you cannot tell from the plan listing, because this detail is rarely published alongside the allowance and validity. The most direct route is to ask before buying; where there is no confirmed information we will say so rather than guess. The alternative is to test on arrival by turning Wi-Fi off and seeing which country an IP-location page reports.

Not necessarily. Raw download speed can still be perfectly good. What suffers more visibly is responsiveness, which shows up as pages hesitating before they load or app calls feeling delayed. For everyday use such as maps and messaging the difference may not bother you; for video meetings it is far more noticeable.

Not always. Try setting the language inside the site or app first, since many services remember your choice and stop guessing from location. If the annoyance is only language and currency, a setting usually ends it. If you need services to genuinely see you in the destination country, that is a different matter and may mean choosing another plan next time.

It does not. SMS codes travel over the telephone network, not the internet. What decides whether you receive them is whether your Thai SIM is still active in the handset and how that line is configured. Most travel data plans are data-only with no number for receiving SMS, so plan the two things separately.

Not necessarily, because in each country the handset may attach to a different network and the arrangements behind them differ. What you observe in the first country is no guarantee for the next. If it matters, repeat the check after each border, and do not generalise from a single result.

A VPN does change the location sites see, but it does nothing for latency and usually adds to it, since traffic passes through an extra server. Some services also have their own terms about this, which you should read yourself. We do not advise on which services to use one with.