first of all, I think you should be asking the difference between 国家 and 国"country" & 语言 and 语(not 言)"language",right? I'd tried several translator, none of it translate 言 to "language". Ok,back to the topic. 国家 is country. 国 always goes with another ( some other) character to bring out the meaning of "country". like 英国 England [country] 美国 America [country] 法国 France [country] 国土 Homeland [land of the country] 国王 King [king of the country] same,语言 is language. 语 always goes with another ( some other) character to bring out the meaning of "language". like 英语 [English] 美语 [American] 法语 [French] 词语 [word group] 语句 [sentence]

国家with 国"country" & 语言with 言 ================================== 例子1 中国是一个发展中国家 China is a developing country 中国=China; 一个=a=one；发展中=developing; 国家=country 【发达国家=developed country】 例子2 国 usually we use it in idomatic phrase. For example, 国中之国=a country which is inside of another country 【like vanticano, in Italy】 中=inside=centre； 之=的 国王=king； 国=country， 王=king 【in fact , 国王=king of country】 国民=people of the country; 民=people 国家： 国=country；家=family; 国富民强: 富=富裕=rich；民=people；强=强壮=strong 国庆： 庆=庆祝=celebrity。in China the National Day (国庆节）is 1st October. ----------------------------------------- 语言=language 语=word=话；言=speak 例子3 很多中国人说普通话 There are many chinese people who speak Putonghua (Mandrin) 很多=many；中国人=chinese=chinese people；说=speak （in this sentence, you can not say 言普通话, you just say 说普通话）；普通话=Putonghua=mandrin 例子4 言 is used in idiomatic phrase. for example, 言论，言行，言而无信，言之有理，言之凿凿

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In sentences, we usually use "国家" and “语言" to represent 'country' and 'language', Especially 'language'. In daily conversation, we hardly use "言'' to reprent 'language'. E.g. This is a great country. (这是一个伟大的国家。) What language does this system use? (这种系统使用的是哪种语言？)