How to Sum text values like numbers in Numbers?
I found some solution now.

SOLUTION 1 

Use "COUNTIF" function to find the number of cells that match the given text values and then multiply with the reference numbers.



SOLUTION 2 

Use Cell "Data Format"


Select some Cell
At the Format Panel > Cell > Data Format
Create a Custom Format.
Select type as "Number"
Add some Rule that you want to format number as text.
Done! You can sum text values like a number now.




You can also see this if you want to use a pop-up menu