Update i18n docs
Update i18n docs

Mainly adding string interpolation example that came up in a recent PR

SEL-Columbia/commcare-hq,puttarajubr/commcare-hq,puttarajubr/commcare-hq,gmimano/commcaretest,dimagi/commcare-hq,qedsoftware/commcare-hq,gmimano/commcaretest,puttarajubr/commcare-hq,SEL-Columbia/commcare-hq,SEL-Columbia/commcare-hq,gmimano/commcaretest,dimagi/commcare-hq,dimagi/commcare-hq,qedsoftware/commcare-hq,dimagi/commcare-hq,qedsoftware/commcare-hq,dimagi/commcare-hq,qedsoftware/commcare-hq,puttarajubr/commcare-hq,qedsoftware/commcare-hq