fade
bland
Without flavor or with very little flavor; not seasoned enough.
Die Suppe schmeckt etwas fade, es fehlt Salz.
The soup tastes a bit bland; it needs salt.

bland / dull / weak
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bland
Without flavor or with very little flavor; not seasoned enough.
Die Suppe schmeckt etwas fade, es fehlt Salz.
The soup tastes a bit bland; it needs salt.

The German adjective 'fade' means 'geschmacklos' (tasteless/bland) or 'langweilig' (boring/dull). It should not be confused with the English verb 'to fade' (verblassen, schwächer werden).
Ohne Gewürze schmeckt der Reis ziemlich fade.
Without spices, the rice tastes pretty bland.
The exact meaning of 'fade' depends on the noun it describes. With food, it means 'geschmacklos' (tasteless/bland); with events or people, 'langweilig' (boring/dull); and with excuses, 'unglaubwürdig' (unbelievable/unconvincing).
Die Suppe ist fade.
The soup is bland.
In relation to food, 'fade' is often used with 'schmecken' (to taste) or describes typical foods such as 'fade Suppe' (bland soup) or 'fades Essen' (bland food).
Mir schmeckt das Gemüse zu fade, ich brauche mehr Salz.
The vegetables taste too bland to me; I need more salt.
When something is described as boring, typical combinations are 'eine fade Party' (a dull party), 'ein fader Witz' (a dull joke), or 'ein fader Abend' (a dull evening).
Das Gespräch wurde schnell fade, weil er nur über seine Arbeit sprach.
The conversation quickly became dull because he only talked about his work.
The combination 'eine fade Ausrede' (a weak excuse) is a very fixed and common phrase. It expresses that an excuse or explanation is transparent and not convincing.
Er kam mit einer faden Ausrede, warum er zu spät war.
He came up with a weak excuse for why he was late.
interesting
'interessant' and 'fade' are opposites here. 'interessant' describes something that makes you curious or keeps your attention. 'fade' describes something dull, uninteresting, or without variety. You use 'interessant', for example, for a good topic, an exciting exhibition, or a lively conversation. 'fade' is more appropriate when something seems tired, monotonous, or without appeal. 'fade' can also describe taste, but in this relationship the focus is on its contrast with 'interessant'.

Zu Hause wirkt der Abend fade, weil niemand etwas unternehmen möchte.
At home, the evening feels dull because no one wants to do anything.
Meine Nachbarin erzählt mir heute eine interessante Geschichte aus dem Krankenhaus.
Today my neighbor is telling me an interesting story from the hospital.