"I am pleased you travel in this season."
Translation:Je suis heureux que vous voyagiez en cette saison.
Firstly, I think the English sentence is rather awkward and ambiguous. The English sentence could mean that the person is:
(a) travelling throughout the time period such as in generally travelling around
(b) travelling at some point during the time period to achieve a specific goal. For example: I am pleased you are travelling back to Scotland this week to be at my wedding.
If it is case (b) then I think you can drop the preposition en. For example, a more illustrative example would be:
Je suis heureux que vous voyagiez cette semaine - I am pleased you are travelling this week
If it is case (a) then I don't think you can drop the preposition en. For example a more illustrative example would be:
I am pleased you are travelling in this time period. Here the word in cannot be dropped and I suspect it cannot be dropped in the French translation either.
Therefore including or dropping the word in may change the meaning of the sentence.
Also note that
when the preposition in expresses a period of time during which an event happens then in is translated as:
dans when used to express an amount of time before something will happen
en when used to indicate how long something takes.
le film est dans trois heures the movie is in 3 hours.
Je vais manger mon repas dans dix minutes. I will eat my meal in ten minutes
J'ai mangé mon repas en dix minutes. I ate my meal in ten minutes
Je peux faire mes devoirs en trois minutes I can do my homework in three minutes.
Elle était capable de résoudre le problème en dix minutes. She was able to solve the problem in ten minutes.