Nintendo announced back in January that the Switch would not be region locked, allowing you to import and play games from other countries. It seems that you will also be able to access the eShop from other regions, although there are some caveats that may limit this ability.
With the day-one update live, Switch users can now access the eShop, add friends (using friend codes), and more. This has led to the discovery that you can sign into the eShop from other regions, including Japan, where there are traditionally a plethora of a games released that never make their way overseas. This is done by making a profile on the system and connecting it to a new Nintendo Account account that is set to the region whose eShop you want to access.
Logging in to this profile on the system and going to the eShop then shows you games from the market. If you make a Japanese account, it will let you access certain things not available in North America or Europe at the present time, including Puyo Puyo Tetris and New Frontier Days: Founding Pioneers, according to Eurogamer.
However, you reportedly cannot purchase games from other regions with a debit or credit card from a different country. It is possible that purchasing prepaid cards will be a workaround for this, but this information remains unconfirmed.
However, you can download free demos from other regions, which would include Japan’s Puyo Puyo Tetris demo, for instance. In addition, journalist Chris Kohler noted on Twitter that Japanese eShop games may even feature English text options.