Here is a list of them:
Some countries of seven letters where French is an official language would be Belgium, Senegal, Burundi, Comoros & Vanuatu.
There are 33 countries that have seven letters in their English names. These countries include Ukraine, Senegal, Lebanon, Jamaica, and Ireland to name a few.
There are no countries (in English) with names five letters long with "s" as the second letter.
Virtually all countries have 3 letters in their names.
BulgariaMongoliaPortugalSlovakiaSlovenia
BeninChileChinaEgyptGabonGhanaHaitiIndiaItalyJapanKenyaLibyaMaltaNauruNepalNigerPalauQatarSamoaSpainSudanSyriaTongaYemen
There are over 30 countries in the world with eight letters in the names. Examples of these countries include Barbados, Botswana, Bulgaria, Cambodia, Colombia, Ethiopia, and Hong Kong.
There are 33 countries that have seven letters in their English names. These countries include Eritrea, Finland, Denmark, Ecuador, Somalia, and Nigeria to name a few.
BrazilAngolaGambiaMalawiJordanBhutanCyprusRwandaZambiaNorwayRussiaPolandMonacoLatviaFranceGreeceBosniaGuyanaPanamaTuvaluBelizeCanadaMexicoSwedenGuineaTurkeyItalia ?Espana?
AlbaniaAlgeriaAndorraArmeniaAustriaBahamasBahrainBelarusBelgiumBoliviaBurundiComorosCroatiaDenmarkEcuadorEritreaEstoniaFinlandGeorgiaGermanyGrenadaHungaryIcelandIrelandIsraelJamaicaLebanonLesothoLiberiaMaldivesMoldovaMoroccoMyanmarNamibiaNigeriaRomaniaSenegalSomaliaTunisiaUkraineUruguayVanuatuVietnam
Denmark
Eritrea