You leave in four weeks. You will not be fluent and you do not need to be. What you need is the ability to handle about fifteen predictable situations without switching to English, and that is genuinely achievable in a month.
List the situations, not the vocabulary
Write down what will actually happen: arriving somewhere, ordering, paying, asking directions, buying a ticket, explaining a problem in a room, saying you have an allergy, asking for the bill. Each situation needs about four sentences. That is sixty sentences for the whole trip — a month of work, not a year.
Learn whole sentences, not words
Under pressure nobody assembles grammar. They reach for a phrase they already own, complete. Memorise the complete sentence, including the polite opening, because that is the part that freezes people. Include the reply you expect. Knowing how to ask is only half of it; most breakdowns happen when the answer arrives.
Practise the numbers harder than anything else
Prices, platform numbers, times, room numbers, quantities. These are the highest-stakes things you will hear and the ones learners reliably miss, because they are spoken fast and never in the order you rehearsed. Drill them until you can catch them at speed. This is worth more than any other single hour you spend.
Skip the tenses
The past and the future are almost unnecessary for four weeks of travel. The present, a few polite forms and the words for yes, no, please and sorry will carry nearly everything. Time spent on conjugation tables is time not spent making your fifteen situations automatic.
Aim to be understood, not correct. Sixty well-drilled sentences and confident numbers will get you further than a term of general study.