the narrator can increase immediacy and urgency by switching into the
present tense.
John le Carré employs this technique (switching from past to present) throughout A Perfect Spy, the book considered by many (including le Carré himself) to be his masterpiece. Most often, he uses it to signal flashbacks, but sometimes it is employed to raise the tension ever so slightly. An example of this occurs in the opening chapter. For context, the protagonist, the traitor Magnus Pym, has slipped away to his own private safe house, a room in a nondescript boarding house. After settling into his room, Pym's tradecraft kicks in:
Suddenly needing an activity, he switched out the lights, slipped
quickly to the window, opened the curtains and set to work checking
out the little square, life by life and window by window as the
morning woke it, while he searched for tell-tale signs of watchers. In
her kitchen, the wife of the Baptist minister, wearing her lovat
dressing-gown, is unpegging her son’s football gear from the washing
line in preparation for today’s match. Pym draws back swiftly. He has
caught a glint of steel in the manse gateway, but it is only the
minister’s bicycle still chained to the trunk of a monkey-puzzle tree
as a precaution against unchristian covetousness. In the frosted
bathroom window of Sea View a woman in a grey slip is stooped over a
handbasin soaping her hair. Celia Venn, the doctor’s daughter who
wants to paint the sea, is evidently expecting company today. Next
door to her at number 8 Mr. Barlow the builder and his wife are
watching breakfast television. Pym’s eye passes methodically on, until
a parked van holds his attention. The passenger door opens, a girlish
figure flits stealthily through the central gardens and vanishes into
number 28. Ella, the daughter of the undertaker, is discovering life.
Pym closed the curtains and put the lights back on...
To me, the sudden switch to present tense (with the second sentence) injects a subtle sense of immediacy which serves to raise the tension just a notch: has Pym been followed? But le Carré was a masterful writer (in my opinion, anyway!) and it requires deft handling.
As a postscript, though, it may be worth noting that for all his skill with English prose, le Carré was a lifelong student and admirer of German. I mention this because the original post specifically raised the use of this technique in German. Le Carré began learning the language at 13. Later, he would describe the first time he heard German as "love at first sound", saying: "I discovered that the language fitted me. It fitted my tongue. It pleased my Nordic ear."
Whether le Carré was conscious of how this technique is used in German, and whether that led to or influenced his use of it in English, will remain a mystery. But it is certainly interesting.