I made a list of country names in Selvesco. It's again based on Loqu's list, but I added a few countries and on a whim did the four countries of the UK. I also put a demonym under each entry.
The demonyms work as nouns, adjectives, and language names when applicable. The demonyms ending in <-o> are made feminine by changing the <-o> to <-a>. The demonyms ending in <-és> are made feminine by changing the ending to <-esa>, but that is only done when they are used nominally (
una fema francés "a French woman" vs.
una Francesa "a female French person").
Germany - Germanha [dʑɛɾˈmaɲa] [dʑəɾˈmaɲa]
German - Germango [dʑɛɾˈmaŋgo] [dʑəɾˈmãːgə]
France - Francza [ˈfɾantɕa] [ˈfɾãːtɕa]
French - Francés [fɾanˈtɕɛs] [fɾãˈtɕeː]
Italy - Italha [ɪˈtaɪ̯a] [iˈtaʎa]
Italian - Italhano [ɪtaˈɪ̯ano] [itaˈʎanə]
Andalusia - Andalusgza [andaˈlʊʑa] [ãdaˈluʑa]*
Andalusian - Andalusgzano [andalʊˈʑano] [ãdaluˈʑanə]
United Kingdom - Renho Unido [ˈreɲo ʊˈnɪdo] [ˈreɲuˌnidə]
Great Britain - Gránt Bretanha [ˈgɾant bɾeˈtaɲa] [ˈgɾãːt bɾiˈtaɲa]
British - Bretango [bɾeˈtaŋgo] [bɾiˈtãːgə]
England - Anguia [ˈaŋgɪ̯a] [ˈãːgja]
English - Anglés [aŋˈglɛs] [ãˈgleː]
Scotland - Escocza [ɛsˈkotɕa] [iːˈkotɕa]
Scottish - Escocés [ɛskoˈtɕɛs] [iːkuˈtɕeː]
Wales - (Paés de) Gales [paˈɛs de ˈgalɛs] [paˈeː ˈdgaliː]
Welsh - Galés [gaˈlɛs] [gaˈleː]
Northern Ireland - Irlanda del Borál [irˈlanda dɛl boˈɾal] [irˈlãːda di buˈɾaw]
Northern Irish - Irlandés Borál [irlanˈdɛs boˈɾal] [irlãˈdeː buˈɾaw]
Ireland - Irlanda [ɪrˈlanda] [irˈlãːda]
Irish - Irlandés [ɪrlanˈdɛs] [irlãˈdeː]
Spain - Espanha [ɛsˈpaɲa] [iːˈpaɲa]
Spanish - Espanhuolo [ɛspaˈɲulo] [iːpaˈɲuːlə]
Portugal - Portogál [pɔɾtoˈgal] [pəɾtuˈgaw]
Portguese - Portogués [pɔɾtoˈgɛs] [pəɾtuˈgeː]
Belgium - Belgza [ˈbɛldʑa] [ˈbɛwdʑa]
Belgian - Belga [ˈbɛlga] [ˈbɛwga]
Switzerland - Helvecza [ɛlˈvetɕa] [əwˈvetɕ] ~or~ Suïssa [ˈsʊ̯ɪsa] [ˈswisa]
Swiss - Suïsso [ˈsʊ̯ɪso] [ˈswisə]
Austria - Uostria [ˈustɾɪ̯a] [ˈuːtɾja]
Austrian - Ostriaco [ɔsˈtɾɪ̯ako] [uːˈtɾjakə]
Hungary - Honguiera [ɔŋˈgiɾa] [ə̃ˈgiːɾa]
Hungarian - Honguerés [ɔŋgeˈɾɛs] [ə̃giˈɾeː]
Greece - Griecza [ˈgɾitɕa] [ˈgɾiːtɕa]
Greek - Griego [ˈgɾigo] [ˈgɾiːgə]
Netherlands - Holanda [oˈlanda] [uˈlãːda] ~or~ Paeses Basos [paˈezɛs ˈbasɔs] [paˈeziː ˈbasuː]
Dutch - Holandés [olanˈdɛs] [ulãˈdeː]
Finland - Finlanda [fɪnˈlanda] [fĩˈlãːda]
Finnish - Finés [fɪˈnɛs] [fiˈneː]
Russia - Ruscza [ˈrʊɕa] [ˈruɕa]
Russian - Russo [ˈrʊso] [ˈrusə]
Sweden - Suecza [ˈsʊ̯etɕa] [ˈswetɕa]
Swedish - Sueco [ˈsʊ̯eko] [ˈswekə]
Norway - Norvegza [nɔrˈvedʑa] [nərˈvedʑa]
Norwegian - Norvego [nɔrˈvego] [nərˈvegə]
Iceland - Islanda [ɪsˈlanda] [iːˈlãːda]
Icelandic - Islandés [ɪslanˈdɛs] [iːlãˈdeː]
Malta - Malta [ˈmalta] [ˈmawta]
Maltese - Maltés [malˈtɛs] [mawˈteː]
USA - Estados Unidos [ɛsˈtadɔs ʊˈnɪdɔs] [iːˈtaduh‿uˈniduː]
US American - Americano [ameɾɪˈkano] [amiɾiˈkanə] ~or~ Estadunidés [ɛstadʊ̯nɪˈdɛs] [iːtaduniˈdeː]
Mexico - Méscico [ˈmeɕɪko] [ˈmeɕikə]
Mexican - Mescicano [meɕɪˈkano] [meɕiˈkanə]
Brazil - Brazilha [bɾaˈzɪɪ̯a] [bɾaˈziʎa]
Brazilian - Brazilhano [bɾazɪˈɪ̯ano] [bɾaziˈʎanə]
Chile - Cile [ˈtɕɪle] [ˈtɕilə]
Chilean - Cileano [tɕɪleˈano] [tɕiliˈanə]
Canada - Cánada [ˈkanada]
Canadian - Canadés [kanaˈdɛs] [kanaˈdeː]
Argentina - Argentina [aɾdʑɛnˈtɪna] [aɾdʑə̃ˈtina]
Argentinian - Argentino [aɾdʑɛnˈtɪno] [aɾdʑə̃ˈtinə]
China - Cina [ˈtɕɪna] [ˈtɕina]
Chinese - Cinés [tɕɪˈnɛs] [tɕiˈneː]
Japan - Gzapón [dʑaˈpɔn] [dʑaˈpɔ̃ː]
Japanese - Gzaponés [dʑapoˈnɛs] [dʑapuˈneː]
India - India [ˈɪndɪ̯a] [ˈĩːdja]
Indian - Indiano [ɪnˈdɪ̯ano] [ĩˈdjanə]
Egypt - Egeto [eˈdʑeto] [iˈdʑetə]
Egyptian - Egeczano [edʑeˈtɕano] [idʑiˈtɕanə]
Australia - Australha [aʊ̯sˈtɾaɪ̯a] [awˈtɾaʎa]
Australian - Australhano [aʊ̯stɾaˈɪ̯ano] [awtɾaˈʎanə]
New Zealand - Nuova Zelanda [ˈnuva zeˈlanda] [ˈnuːva ziˈlãːda]
New Zealander - Neozelandés [neozelanˈdɛs] [niuzilãˈdeː]
Fiji - Figi [ˈfɪdʑɪ] [ˈfidʑi]
Fijian - Figzano [fɪˈdʑano] [fiˈdʑanə]
French Polynesia - Polinesgza Francés [polɪˈneʑa fɾanˈtɕɛs] [puliˈneʑa fɾãˈtɕeː]
French Polynesian - Francopolinesgzano [fɾaŋkopolɪneˈʑano] [fɾãkupuliniˈʑanə]
* Occupied Iberian Republic of Andalusia - República Iverana Ocovada de Andalúsgza [reˈpʊblɪka͡ɪveˌɾana͡okoˌvada de͡andaˈlʊʑa] [riˈpublika͡iviˌɾana͡ukuˌvada dãdaˈluʑa]
EDIT: Updating Orthography