In a certain code language, 'DICE' is written as 'EKFI' and 'PLAN' is written as 'QNDR'. How will 'LUDO' be written in that same language?

Let's check the positional shift pattern between the words and their codes:
For 'DICE' $\to$ 'EKFI':

* $\text{D (4)}\stackrel{+1}{\to }\text{E (5)}$
* $\text{I (9)}\stackrel{+2}{\to }\text{K (11)}$
* $\text{C (3)}\stackrel{+3}{\to }\text{F (6)}$
* $\text{E (5)}\stackrel{+4}{\to }\text{I (9)}$
The pattern of addition is $+1,+2,+3,+4$.

Let's verify with 'PLAN' $\to$ 'QNDR':

* $\text{P (16)}\stackrel{+1}{\to }\text{Q (17)}$
* $\text{L (12)}\stackrel{+2}{\to }\text{N (14)}$
* $\text{A (1)}\stackrel{+3}{\to }\text{D (4)}$
* $\text{N (14)}\stackrel{+4}{\to }\text{R (18)}$

Applying the same pattern to 'LUDO':

* $\text{L (12)}\stackrel{+1}{\to }\text{M (13)}$
* $\text{U (21)}\stackrel{+2}{\to }\text{W (23)}$
* $\text{D (4)}\stackrel{+3}{\to }\text{G (7)}$
* $\text{O (15)}\stackrel{+4}{\to }\text{S (19)}$

Thus, 'LUDO' is coded as 'MWGS'.