Actually I put all the countries of Central America together, because it is only about the visa requirements. For all the other important stuff like vaccinations you can read on “Preparing for Mexico“.
There is no visa required for members of the European Union (EU). The full list you will find here: Visa requirements. You anyway need a valid passport and it must be valid for almost three more month. You also should have a return (onward) ticket and sufficient funds to cover your stay.
The first term of stay is for one month only. “If you decide you really like Belize and would like to stay longer, you can request a one-month extension from the Immigration and Nationality Department. Prospective immigrants renew every month or eventually decide to apply for Belize Permanent Residency.” (Source: https://www.belize.com/belize-visa)
By the way in Belize the population speak English as well as Spanish.
You may stay for 90 days and you do not need a visa if you are an European citizen (EU member) and living there. Your passport must at least be valid for 90 more days, but it is strongly recommended to travel with 6 months validity.
But be aware the Central America 4 Border Control Agreement (El Salvador, Guatemala, Honduras, Nicaragua). You are free to travel in all of these countries for 90 days in all with only one border control (like the Schengen agreement). An extension for 90 days is possible, but there are a lot of additional requirements.
See Guatemala, but it is not a part of the Central America-4 Border Control Agreement. Though you can stay additional 90 days there after the law of Costa Rica.
“Panama tourist visa is not required for citizens of Sweden (and other EU members) for a stay up to 180 days. All travelers will need a passport valid for at least 90 days following your departure date from Panama.” (Source: https://panama.visahq.com/requirements)