SMath Studio has a very interesting Multilanguage support. First of all, the language Interface could be changed (
Tools=>Options=>Interface).

Suppose the English language is selected. Now, insert some text region. Click into it with the left mouse button. Then, click into it with the right mouse button. One of the option is
Choose language. Choose one of the language on the list.

The empty "insert text" cursor will appear.

Type the desired text in the chosen language.

When finished, click outside the text region. Then, point the text. You will see the previous English text as tooltip.

Left click, then right click and choose English language. See the picture.

This way you can add more than one language.

All the text in one language could be changed at once by choosing the desired
Interface language
NOTE: If your language is not on the list, see the SMath forumhow to add it.