I guess that these strings will have always the same number of parameters, even if they can change. For example, today template is "Hi {name}", and tomorrow could be "Hello {name}".

Short answer: No, you cannot do what you have proposed.

Alternative 1: use the string.Format method.

You can store in your database something like this:

"Hi {0}"

Then, when you retrieve the string template from the db, you can write:

var template = "Hi {0}"; //retrieved from db
var name = "Joe";
var result = string.Format(template, name);
//now result is "Hi Joe"

With 2 parameters:

var name2a = "Mike";
var name2b = "John";
var template2 = "Hi {0} and {1}!"; //retrieved from db
var result2 = string.Format(template2, name2a, name2b);
//now result2 is "Hi Mike and John!"

Alternative 2: use a placeholder.

You can store in your database something like this:

"Hi {name}"

Then, when you retrieve the string template from the db, you can write:

var template = "Hi {name}"; //retrieved from db
var name = "Joe";
var result = template.Replace("{name}", name);
//now result is "Hi Joe"

With 3 parameters:

var name2a = "Mike";
var name2b = "John";
var template2 = "Hi {name2a} and {name2b}!"; //retrieved from db
var result2 = template2
    .Replace("{name2a}", name2a)
    .Replace("{name2b}", name2b);
//now result2 is "Hi Mike and John!"

Pay attention at which token you choose for your placeholders. Here I used surrounding curly brackets {}. You should find something that is unlikely to cause collisions with the rest of your text. And that depends entirely on your context.

This can be done as requested using dynamic compilation, such as through the Microsoft.CodeAnalysis.CSharp.Scripting package. For example:

var name = "Joe";
var template = "Hi {name}";
var result = await CSharpScript.EvaluateAsync<string>(
    "var name = \"" + name + "\"; " +
    "return $\"" + template + "\";");

Note that this approach is slow, and you'd need to add more logic to handle escaping of quotes (and injection attacks) within strings, but the above serves as a proof-of-concept.

No you can't do that since it needs name value at the time string is created (compile time). Consider using String.Format or String.Replace instead.