Seems an odd mix of imperial and metric
Assuming latter are mm it translates to 26“ x 1.9-2.1” which makes sense in terms of typical mtn bike tyre sizes used in UK from late 90s to mid 00s. I used tyres that size around that time.
The 26” mtn bike tyre size in UK is ETRTO 559.
Therefore I’d say you are looking for 49-559 to 54-559 in ETRTO.