Characters have a script associated with them (e.g. Latin), and caseness is also part of a character's properties. Now, language-specific subsets¹ of those are

Characters have a script associated with them (e.g. Latin), and caseness is also part of a character's properties. Now, language-specific subsets¹ of those are a bit iffy to deal with. Especially when text can contain loan words from other languages, so in my experience it's rarely a useful thing to ask for. ¹ Yes, subsets. Latin letters lowercase is not the set abcdefghijklmnopqrstuvwxyz. It is the set abcdefghijklmnopqrstuvwxyzªºßàáâãäåæçèéêëìíîïðñòóôõöøùúûüýþÿ āăąćĉċčďđēĕėęěĝğġģĥħĩīĭįıijĵķĸĺļľŀłńņňʼnŋōŏőœŕŗřśŝşšţťŧũūŭůűųŵ ŷźżžſƀƃƅƈƌƍƒƕƙƚƛƞơƣƥƨƪƫƭưƴƶƹƺƽƾƿdžljnjǎǐǒǔǖǘǚǜǝǟǡǣǥǧǩǫǭǯǰdzǵǹǻǽǿ ȁȃȅȇȉȋȍȏȑȓȕȗșțȝȟȡȣȥȧȩȫȭȯȱȳȴȵȶȷȸȹȼȿɀɂɇɉɋɍɏɐɑɒɓɔɕɖɗɘəɚɛɜɝɞɟɠɡɢ ɣɤɥɦɧɨɩɪɫɬɭɮɯɰɱɲɳɴɵɶɷɸɹɺɻɼɽɾɿʀʁʂʃʄʅʆʇʈʉʊʋʌʍʎʏʐʑʒʓʕʖʗʘʙʚʛʜʝʞʟ ʠʡʢʣʤʥʦʧʨʩʪʫʬʭʮʯʰʱʲʳʴʵʶʷʸˠˡˢˣˤᴀᴁᴂᴃᴄᴅᴆᴇᴈᴉᴊᴋᴌᴍᴎᴏᴐᴑᴒᴓᴔᴕᴖᴗᴘᴙᴚᴛᴜᴝ ᴞᴟᴠᴡᴢᴣᴤᴥᴬᴭᴮᴯᴰᴱᴲᴳᴴᴵᴶᴷᴸᴹᴺᴻᴼᴽᴾᴿᵀᵁᵂᵃᵄᵅᵆᵇᵈᵉᵊᵋᵌᵍᵎᵏᵐᵑᵒᵓᵔᵕᵖᵗᵘᵙᵚᵛᵜᵢᵣᵤ ᵥᵫᵬᵭᵮᵯᵰᵱᵲᵳᵴᵵᵶᵷᵹᵺᵻᵼᵽᵾᵿᶀᶁᶂᶃᶄᶅᶆᶇᶈᶉᶊᶋᶌᶍᶎᶏᶐᶑᶒᶓᶔᶕᶖᶗᶘᶙᶚᶛᶜᶝᶞᶟᶠᶡᶢᶣᶤᶥᶦ ᶧᶨᶩᶪᶫᶬᶭᶮᶯᶰᶱᶲᶳᶴᶵᶶᶷᶸᶹᶺᶻᶼᶽᶾḁḃḅḇḉḋḍḏḑḓḕḗḙḛḝḟḡḣḥḧḩḫḭḯḱḳḵḷḹḻḽḿṁṃṅṇ ṉṋṍṏṑṓṕṗṙṛṝṟṡṣṥṧṩṫṭṯṱṳṵṷṹṻṽṿẁẃẅẇẉẋẍẏẑẓẕẖẗẘẙẚẛẜẝẟạảấầẩẫậắằẳẵặẹ ẻẽếềểễệỉịọỏốồổỗộớờởỡợụủứừửữựỳỵỷỹỻỽỿⁱⁿₐₑₒₓₔₕₖₗₘₙₚₛₜⅎↄⱡⱥⱦⱨⱪ ⱬⱱⱳⱴⱶⱷⱸⱹⱺⱻⱼⱽꜣꜥꜧꜩꜫꜭꜯꜰꜱꜳꜵꜷꜹꜻꜽꜿꝁꝃꝅꝇꝉꝋꝍꝏꝑꝓꝕꝗꝙꝛꝝꝟꝡꝣꝥꝧꝩꝫꝭꝯꝰꝱꝲꝳꝴꝵ ꝶꝷꝸꝺꝼꝿꞁꞃꞅꞇꞌꞎꞑꞓꞡꞣꞥꞧꞩꟸꟹꟺfffiflffifflſtstａｂｃｄｅｆｇｈｉｊｋｌｍｎｏｐｑｒ ｓｔｕｖｗｘｙｚ How do you condense that again into language-specific subsets? Every letter that appears in a word in a dictionary? Then at least é belongs to German as well, even though it's usually not considered part of the German Latin subset. Unicode stays clear of that issue by simply not defining what script subsets a character belongs to (rightfully so, IMHO).