Which part is the root you mentioned. "denmark" or "denmark.handa"?
Could you supply more "real" examples. For example, is the the ".[[:digit:]]-" always ".1-"?
You need to be as precise as possible in defining an input pattern and it's position in the line to prevent false positives or prevent missing a matching pattern.
Also what is the encoding scheme. You may need to use [[:alpha:]] instead of [a-z] for example to include accents.
sed 's/ \([[:alpha:]][[:alpha:]]*\.[[:alpha:]][[:alpha:]]*\.[[:digit:]]-[[:digit:]][[:digit:]]*\) /\1_1/' file
This example assumes that the initial digit is alway only one digit in length, but might be between 0-9, and that there will always be a space before and after the the pattern. Sometimes you will have more than one line to handle different input patterns. One thing to look out for is if the pattern might be split between two lines. This will complicate things greatly because then you will need to save some lines in the buffer and then check for matching patterns depending on where the split is. Then you also need to decide whether to add the "_1" to the end leaving the line split, or move the line split.