Romansh (also spelled Romansch or Romanche) is a term that covers various Gallo-Romance languages spoken in Switzerland. They are closely related to other Gallo-Romance idioms spoken in Italy, Switzerland and France. Romansh was standardized in the last century. On the orthographic level, Heinrich Schmidt sought to avoid all 'odd-looking' spellings, in order to increase general acceptability of the new idiom and its spelling. Therefore, words with /c/ plus /e, i/ have <tg> (tgirar) instead of <ch>. Words with /c/ followed by /a, o, u/ have <ch> (chalanda) as both speakers of Engadin (chalanda) and the Rhine territory (calanda) except a spelling with <c->. At the same time, che and chi are – due to this rule, called "Leza Uffers Kompromiss" – pronounced /ke/ and /ki/. <k> on the other hand would be a grapheme deemed unfit for a Romance tongue such as Romansh. Schwa, however, is represented by <e> in RG which makes it closer to German, as does the use of <sch> for both /S/ and /Z/ and <tsch> for /tS/.
On the other hand, the fact that there is no <ü, ö> in RG may not only be due to the lack of /y/ and /2/ in most Romansh idioms, but also to the graphic form which is seen as non-Romance. This also shows that it is not always phonetics that leads to the adoption of a new grapheme, but sometimes also the lack of a grapheme that leads to a certain phonetic shape of the standard. All in all, RG spelling is a compromise between Romance (Italian, French) and Germanic (German) spelling.
The Lia Rumantscha (http://www.liarumantscha.ch) is the umbrella organization for all Romansh associations. Their web site provides further background information.
See also dialect.